METHODS AND COMPOSITIONS FOR SALMONELLA-BASED VACCINES

Abstract: Isolated nucleic acid molecules comprising one or more of the sefB, sefC, sefD, sefU?1?, sefU?2?, agfA, tctA, tctB, or tctC genes of Salmonella. Isolated proteins encoded by said genes. Methods and compositions for eliciting an immune response in animals utilizing the isolated genes and/or proteins, including the utilization of attenuated Salmonella, E. coli, Shigella and other bacteria produced pursuant to induced mutuations in certain of the described genes.

Description: Description METHODS AND COMPOSITIONS FOR SALMONELLA -BASED VACCINES Cross-Reference To Related Applications This application is a continuation-in-part of United States patent application Serial No. 08/054,452, filed April 26, 1993 and presently pending. Technical Field The present invention relates generally to methods and compositions for eliciting an immune response, and more particularly to such compositions directed to, or based on, Salmonella. Background of the Invention In 1980, the World Health Organization estimated that in developing countries food poisoning from infection with Salmonella bacteria (salmonellosis) contributed in a major way to food borne infections resulting in more than 1 billion cases of acute diarrhea in children under the age of five years (Kvenberg and Archer, Food Technol. 40:11-9%, 1987, and at least 5 million deaths (this reference, and all other references cited herein, is hereby expressly incorporated herein by reference in its entirety). Since the mid-1980s, the worldwide incidence of salmonellosis has increased steadily. S. enteritidis (also known as S. enterica ser. Enteritidis), in particular, has been implicated in the sharp increase in food borne infection in industrialized countries since 1983. Indeed, the current frequency of 5. enteritidis infections is considered to constitute a worldwide pandemic (Rodrigue et al., Epidemiol. Infect. 705:21-27, 1990). The severity of the disease is greatest in infants, the elderly, the infirm and in other persons with inadequate or impaired immune systems, including the malnourished. In third world countries where malnutrition is more commonly a complicating factor, mortality rates due to S. enteritidis infection as high as 28% have been reported. In both the clinical and industrial settings, the. situation is also complicated by the fact that many people are asymptomatic carriers. Salmonella spp., including S. enteritidis, often possess several plasmid encoded antibiotic resistance genes that complicate the treatment of human infections. In the industrialized world, it is the contamination of food products by Salmonella bacteria that is most directly threatening to human health. Hence, it is not surprising that the increase in salmonellosis in first world countries parallels the centralization of food production and processing despite continued improvements in epide iological and microbiological methods. The significance of the problem is reflected in one aspect in the poultry- related industries. For example, in the U.S. alone hatcheries produce approximately 100 million broiler chicks per week and chicken egg production in the U.S. has reached 5 billion annually. A large proportion of S. enteritidis infections have been associated with the contamination of the contents of whole shell eggs resulting from vertical transmission of this pathogen due to transovarian infection. This is significant since common procedures designed to decontaminate the external shell surface are not effective. The problem presented by S. enteritidis is exacerbated by the feet that infection in the adult laying hens may be asymptomatic. Typically, S. enteritidis infection of laying birds does not have a significant adverse effect on fertility, hatchability or egg production. Similarly, broiler chickens may be asymptomatic throughout their lifetime, although losses of about 20% do occur in infected flocks due to death in chicks, retardation of growth and rejection of contaminated birds at slaughtering. Contaminated poultry feed may be a major source of infection, but stress to poultry due to handling, transportation and overcrowding add to the problem by increasing the shedding of Salmonella from infected chickens. The end result is that the majority of modern processing plants, which process about 10,000 birds per hour, are contaminated and Salmonella are typically isolated from 40% to 70% of turkey or chicken carcasses sampled in the U.S. and Canada (Lammerding et al. J. Food Protection 51:41, 1986). The overall economic costs of the rising incidence of food bome infections have been significant. The U.S. General Accounting Office has recently estimated the cost of S. enteritidis food poisoning in the U.S. between 1985 to 1990 at $118 million in lost productivity, medical and hospital costs resulting from about 9,500 illnesses. The U.S. Center for Disease Control receives more than 40,000 case reports annually but attributes greater than 2 million cases and roughly 2,000 deaths per year in the United States to salmonellosis (Cohen and Tauxe, Science 234:964-969, 1986). The economic cost related to treatment of salmonellosis in the U.S. was estimated to be $50 million in 1986. About 8 million cases involve physician consultation and an estimated 250,000 cases require hospitalization. Non-hospitalized cases are thought to have accounted for about $680 million in medical costs and minimally $2 billion in lost productivity. Others estimate the total costs of salmonellosis in the U.S. arising from medical treatment and lost productivity to be as high as $23 billion per year (Kvenberg and Archer, supra). The losses absorbed by the food industry from liability and product loss are undoubtedly passed on to the consumer. Thus, there is a need for an effective risk- management program to monitor the different phases of poultry production including breeding, raising, slaughtering, packing and further processing, distribution and preparation, and consumption. The development of strategies for creating Salmonella- free feed, the control of ' Salmonella in breeder flocks, hatcheries, and product operations will include development of more effective diagnostics and vaccines. It is generally accepted that killed Salmonella vaccines are inferior to live attenuated Salmonella vaccines so this method has been more-or-less abandoned as a vaccine strategy. Several reports exist that explore humoral response of the host to Salmonella components but this strategy has not been widely adopted. Some examples include an outer membrane protein preparation with 4% LPS content, which reportedly gave some protection to S. typhimurium in mice (Isibasi et al., Infect. Immun. 5*5:2953, 1988). However, Salmonella fimbriae have not been explored for use as subunit vaccines. Putative vaccines have been developed with S. typhi to prevent typhoid fever in humans. However, several non-typhoid Salmonella spp. which cause gastroenteritis in humans are host-adapted to cause a typhoid-like disease in certain animals. Consequently, attenuating mutations that have been made in one strain have to be transferred to other Salmonella strains to create attenuated mutant vaccines responsive to host-specific diseases. In terms of vaccine design, four basic approaches have been attempted, namely killed vaccine strains, subunit vaccines using purified cell components to elicit protective antibody response, live attenuated strains and live attenuated strains expressing foreign proteins. Several putative vaccines have been devised that express foreign epitopes on the surface of cells of attenuated Salmonella. Some examples include immunogenic epitopes of hepatitis B surface antigens (Wu et al., Proc. Natl. Acad Sci. USA 86:4126- 4730, 1989; Schόdel et al., in Progress in Hepatitis B Immunization, Coursget and Tong, eds., pp. 43-50, 1990), the major surface protein, gp63, of Leishmania (Young et al., J. Immunol. 745:2281-2285, 1990), the Streptococcal M protein (Poirer et al., J. Exp. Med 168:25-32, 1988), and the 31 KDa protein of Brucella abortus (Statel et al., Infect. Immun. 55:2048-2055, 1990). In some instances, foreign epitopes have been presented on flagella through incorporation of foreign DNA into the flagellin protein gene encoded on an expression vector. For example, a cholera toxin epitope has been expressed from a recombinant plasmid in a aroA~, flagellin" strain of 5. dublin (Newton et al., Science 244:10-12, 1989). However, none of these systems include the use of fimbriae or fimbrial gene products in the vaccines. A live attenuated Salmonella vaccine that persists long enough in the host to elicit a long lasting high level immunity is desired. Several attenuating mutations have been identified that have been used in one or more Salmonella spp. singly or in combination for potential use as vaccines. Such vaccines have occasionally shown some protection in mice. However, there has gone unmet a need for vaccine technologies to reduce the problems associated with food borne, and other, salmonellosis. The present invention provides these and other related advantages. Summary of the Invention In one aspect, the present invention provides a composition capable of eliciting an immune response, and preferably a vaccine, comprising an isolated AgfA protein in combination with a physiologically acceptable carrier or diluent. In alternative embodiments, the composition comprises a SefB, SefC, SefD, TctC, TctB or TctA protein. In a further aspect, the present invention provides vector constructs comprising one or more of a mutant tctA gene, tctB gene, tctC gene or the tctl operon that is able to inactivate the corresponding tricarboxylic acid transport pathway in Salmonella, to yield an attenuated Salmonella. Preferably, the vector construct further comprises a mutant gene that inactivates the ability of Salmonella to utilize succinate. Alternatively, the vector construct comprising the mutant tctA, tctB, or tctC gene is used in combination with a vector construct that inactivates the ability of Salmonella to utilize succinate. This aspect of the invention therefore provides a biologically pure, attenuated Salmonella comprising a mutation in its tctA, tctB, or tctC gene, and/or a gene required for succinate utilization This aspect of the invention further provides a composition capable of eliciting an immune response, and preferably a vaccine, comprising an attenuated Salmonella that has an inactivating mutation in one or more of its tctA, tctB, or tctC genes in combination with a physiologically acceptable carrier or diluent. Alternatively, the composition comprises an attenuated Salmonella having an inactivating mutation in one or more of its tc/7 operon (tctDCBA), tctll operon, or tctlll operon. As a further alternative, the Salmonella, either in combination with an attenuating mutation as above or instead of such a mutation, has a mutation in two or more fimbrin encoding genes, such as sefA, sefD, afgA orfimA, wherein the mutation effectively prevents production of fimbriae from such genes. In preferred embodiments, the attenuated Salmonella is able to express a foreign antigen in one or more of its fimbriae. Alternatively, the foreign antigen is fused to a SefA, SefD, SefC, TctA or AgfA protein. The present invention also provides such attenuated Salmonella in a biologically pure form. In yet a further aspect, the present invention provides an expression vector construct comprising an agfA gene that is operably fused in an open reading frame to a foreign gene to yield a dicistronic gene product, the dicistronic gene product able to be expressed in a fimbria of a Salmonella or an aggregate comprising such gene product. By "foreign gene" it is meant a gene that is not typically expressed in open reading frame immediately after the agfA gene, and preferably a gene that is not found in Salmonella in the wild state. Such a foreign gene preferably provides a foreign antigen or epitope, including an immunologically active fragment thereof. In alternative embodiments, the expression vector construct comprises a tctA gene, tctB gene, tctC gene, sefA gene, sefB gene, sefC gene or an sefD gene. In a further alternative embodiment, the fimbria or aggregate is expressed in an E. coli, or in a Shigella spp. In still another alternative embodiment, the expression vector construct comprises an agfA gene, sefA gene or a sefD gene able to produce in E. coli, Shigella or other Enterobacteriaceae a stable fimbria that comprises AgfA protein and/or SefD protein. In still a further aspect, the present invention provides a stable fimbria or aggregate comprising an AgfA, SefA, SefD, SefC, SefB, TctC, TctB or TctA protein fused to one or more foreign antigens. In an alternative embodiment, this aspect of the present invention provides a stable amino acid polymer comprising an AgfA, SefA, SefD, SefC, SefB, TctC, TctB or TctA protein fused to one or more foreign antigens. Within the context of the present invention, such a stable amino acid polymer, preferably formed in part of AgfA, is able to pass as a naked protein through the stomach of an animal without significant degradation. In yet a further aspect, the present invention provides methods of eliciting an immune response in, and preferably vaccinating, an animal. In this aspect, fimbriae or aggregates comprising an AgfA, SefA, SefD, SefC, SefB, TctC, TctB or TctA protein fused to a foreign antigen are separated from their Salmonella host cell, and then introduced into the animal in conjunction with a physiologically, or pharmaceutically, acceptable carrier or diluent. In an alternative embodiment, the host cell is used to grow a stable amino acid polymer comprising one or more of an AgfA, SefA, SefD, SefC, SefB, TctC, TctB or TctA protein fused to a foreign antigen, which polymer may not comprise a fimbria. In a further alternative embodiment, the fimbriae or aggregate are separated from the host cell prior to being introduced into the animal. In still a further alternative embodiment, the fimbria or amino acid polymer comprises an AgfA, SefA, SefD, SefC, SefB, TctC, TctB or TctA protein and are grown in an E. coli host cell or a Shigella host cell. Alternatively, the host cell for the expression vector construct is Citrobacter, Enterobacteria, Pseudomonas, Streptomyces, Bacillus, or Staphylococcus aureus. Preferably, the AgfA, SefA, SefD, SefC, SefB, TctC, TctB or TctA protein of these alternative embodiments is further fused to a foreign antigen. Preferably, the fimbriae or amino acid polymers are introduced orally or via injection to the animal. Further preferably, the fimbriae or amino acid polymers are packaged in protein or biodegradable polymers or copolymers, such as polylactide, polygalactide, polycaprolactone, polyanhydride, polyorthoesters, to form microspheres, or are bound to a substrate protein or bacterium. The fimbriae or amino acid polymers may also be maintained in an array. In yet a further aspect, the present invention provides a method of eliciting an immune response in, and preferably vaccinating, an animal comprising introducing an isolated AgfA protein in combination with a physiologically acceptable carrier into the animal. Preferably, the animal for this method of vaccination, and all other methods of vaccination as described herein, is a human being. In alternative preferred embodiments, the animal is a warm-blooded animal, and further preferably a commercially important warm-blooded animal, including a fowl, a pig, a horse, a dog, a cat, or a cow. In further alternative embodiments, the animal is another commercially important animal such as a shellfish. In alternative embodiments, the isolated protein is a SefD, SefC, SefB, TctC, TctB or a TctA protein In still yet another aspect, the present invention provides methods of eliciting an immune response in, and preferably vaccinating, an animal comprising introducing attenuated Salmonella into the animal. The attenuated Salmonella may comprise one or more of an ineffective tctA gene, tctB gene, tctC gene, tctl operon, tail operon, or tctlll operon, in one embodiment in combination with mutations of the agfA, sefB, sefD or fimA. As noted above, the attenuated Salmonella may alternatively comprise two or more ineffective fimbriae genes. In preferred embodiments, the attenuated Salmonella expresses one or more foreign antigens. In a still further preferred embodiment, the foreign antigen is located on a SEF17 or SEF18 fimbria of the attenuated Salmonella. It is a further feature of this aspect of the invention that the immune response of the animal can be induced by introducing an E. coli into the animal, wherein the E. coli expresses a Salmonella fimbria. Preferably, the Salmonella fimbria comprises an agfA gene product, a sefA gene product or a sefD gene product. Further preferably, the Salmonella fimbria further comprises a foreign antigen. Alternatively, a Shigella is used in place of the E. coli. Further alternatively, another Enterobacteriaceae is used in place of E. coli. In yet a further aspect, the present invention provides a method of eliciting an immune response in, and preferably vaccinating, an animal wherein a nucleic acid vector is introduced into the animal. The vector comprises a sefA gene, sefD gene, sefC gene, sefB gene, tctC gene, tctB gene, tctA gene, or agfA gene. Further preferably, the vector is naked and is injected into a muscle of the animal and/or the above-listed gene is fused to a further, antigen-producing gene to provide an antigenic fusion gene product. These and other aspects of the present invention will become evident upon reference to the following detailed description and attached drawings. In addition, various references are set forth below which describe in more detail certain procedures or compositions {e.g., plasmids, etc.); such references are incorporated by reference in their entirety. Brief Description of the Drawings Figure 1 is a schematic illustration and open reading frame analysis of the sefU2UjABCD gene cluster. Figures 2A-2D depict the nucleotide sequence of sefA, sefB, sefC and sefD, and the corresponding predicted amino acid sequences. Figures 3A-3B depict the nucleotide sequence of sefϋj and sefU2, and the corresponding predicted amino acid sequences. Figures 4A-4B depict the nucleotide sequence of tctA, and the corresponding predicted amino acid sequence. Figure 5 depicts the nucleotide sequence of tctB, and the corresponding predicted amino acid sequence. Figures 6A-6B depict the nucleotide sequence of tctC, and the corresponding predicted amino acid sequence. Figure 7 A depicts the nucleotide sequence of an agfA gene fragment amplified from S. enteritis 27655-3b TτφhoA mutant strain and cloned into pUC19, and the corresponding predicted amino acid sequence. The solid arrows indicate PCR primer pairs TAF3 and TAF4; the dashed arrows indicate TAF5 and TAF6. Figure 7B depicts the nucleotide sequence of agfA, and the corresponding predicted amino acid sequence. Figure 8A depicts an autoradiograph of the results of expression of the sefA, sefB and sefC genes in an £. coli in vitro transcription-translation system. Lane 1, pTZ19; Lane 2, pKXl; Lane 3, pSCl; Lane 4, deIB15; Lane 5, delB23; Lane 6, delDlO; Lane 7, Western blot of the in vitro transcription-translation of pKXl developed using antisera generated against denatured SEF14 fimbrin. The size of the molecular weight markers is indicated on the left (IO 3 M r ). Figure 8B is a schematic representation of the sefgene cluster showing the inserts of various deletion subclones used in the in vitro transcription-translation experiments. ,, Figure 9 depicts an autoradiograph of the mapping of the 5' end of the sefA transcript using primer extension. The lane labeled H S. enteritidis" represents the reverse transcriptase products of RNA isolated from this organism grown in CFA static broth for 60 hours at 37°C. The lanes C, A, T, and G represent the results of dideoxy chain termination sequence reactions in the region encompassing the promoter. The sequence of the γ- 32 P-labeled primer (TGCGTGGGCACTGCCACA) (SEQ ID No. ) is complementary to nucleotides 181-198 of sefA. The arrows indicate two major transcription initiation sites. Figures 10A-C depict immunoelectron microscopy of negatively stained cells for SEF14 production. (A) S. enteritidis 27655-3b; (B) £ coli HB101 carrying cos48; (C) £ coli JM109 carrying pKXl. Magnification: (A) xl 15,000; (B) x94,000; (C) xl44,000. Detailed Description of the Invention The present invention provides methods and compositions for eliciting an immune response from vaccines to Salmonella. These methods and compositions include numerous isolated genes specific to Salmonella, vector constructs, numerous isolated proteins specific to Salmonella and vaccines. These methods and compositions are described further, below. I. Genes Specific to Salmonella A. Genes Generally The present invention provides isolated DNA molecules comprising the sefU2U]ABCD gene cluster, the sefABCD gene cluster, sefBCD gene cluster, se U^Ui gene cluster, the sefA gene, the seβ gene, the sefD gene, the agfA gene, the tctCBA gene cluster, the tctA gene, the tctB gene, and/or the tctC gene. Although one embodiment of each of these molecules is shown in Figures 2 to 7B, it should be understood that within the context of the present invention, reference to one or more of these genes includes derivatives of the genes that are substantially similar to the genes (and, where appropriate, the protein (including peptides and polypeptides) that are encoded by the genes and their derivatives). As used herein, a nucleotide sequence is deemed to be "substantially similar" if: (a) the DNA sequence is derived from the coding region of a native gene of any Salmonella serovar and maintains substantially the same biological activity (including, for example, portions of the sequence or allelic variations of the sequences discussed above); (b) the DNA sequence is capable of hybridization to DNA sequences of the present invention under moderate, high or very high stringency {see Sambrook et al., Molecular Cloning: A Laboratory Manual, 2d ed., Cold Spring Harbor Laboratory Press, NY, 1989); or (c) the DNA sequences are degenerate as a result of the genetic code to the DNA sequences defined in (a) or (b). Within the context of the present invention, moderate stringency means conditions such that an appropriate nucleotide sequence is able to selectively hybridize to nucleotide sequences from Salmonella and to conserved nucleotide sequences in other bacteria such as E. coli. High stringency means the nucleotide sequence is able to selectively hybridize to nucleotide sequences from Salmonella. Very high stringency means the nucleotide sequence is able to selectively hybridize to a single Salmonella species, such as S. enteritidis, S. dublin or S. gallinarum. B. sefA, sefB. sefC. sefD. sefUj. sefϋ eenes and the sefU2lfjABCD operon As can be seen by reference to Figure 1, which is a schematic illustration and open reading frame analysis of the sefU2UjABCD gene cluster, the sefA, sefB, and sefC genes comprise an approximately 3.9 kilobase pair region of Salmonella DNA. In vitro expression directed by the 5.3 kilobase pair DNA fragment of Figure 1 indicated that the SefA, SefB and SefC proteins have an approximately 14 K, 28 K, and 90 KΛ r molecular weight, respectively. See Figure 8A. The present invention involves one or more of a sefA, seβ, sefC, sefD, sefUj, or sefU2 gene or gene cluster. Further information with respect to these genes and their products may be found in U.S. Application Ser. No. 08/054,542. See also Application Ser. No. (attorney's docket no. 920043.403 Cl), and Application Ser. No. (attorney's docket no. 920043.403 C2). As noted above, these applications and all other references cited herein are expressly incorporated by reference herein in their entirety. Experimental results with S. enteritidis indicate that seβ and sefC are not expressed in the absence of sefA. Primer extension analysis of sefABC gene clusters revealed two major transcription start cites located upstream of sefA (Figure 9). Transcription of seβ and sefC is also initiated from the sefA promoter region. Secondary structure analysis of the mRNA transcript from sefABC predicted the formation of two stable stem-loop structures in the intercistroπic region between sefA and seβ, which is indicative of differential regulation of sefA as opposed to seβ and sefC translation. The nucleotide sequences, and corresponding amino acid sequences, of sefA, seβ, sefC, seβ, sefUj and sefU2 are depicted in Figures 2 and 3. sefU j and sefU2 are overlapping open reading frames oriented in the opposite directions {i.e., encoded on opposite strands). sefD abuts sefC and a consensus Shine-Dalga-rno ribosomal binding site sequence is just inside the sefC or f. No promoter is recognized immediately upstream of seβ; expression may be directed by the sefA promoter. C. agfA gene The agfA gene codes for a structural fimbrin protein composing very thin fimbriae, approximately 3-4 nanometers in diameter, that are highly aggregative and stable. The aggregative property of the fimbriae is believed to be due at least in part to its hydrophobicity. The gene product of the agfA gene, AgfA, is found in SEF17 fimbriae, and comprises an approximately 14-15 KΛ r molecular weight fimbrin protein. AgfA contributes to heavy pellicle formation in static cultures, colony hydrophobicity, and autoaggregation of cells in culture. SEF17 fimbriae are immunologically distinct from SEF14 and SEF21, as indicated by the lack of cross-reactivity with polyclonal antisera raised in rabbits against SEF14 or SEF21 (Collinson et al., "Purification and characterization of thin, aggregative fimbriae from S. enteritidis," J. Bacteriol. 773:4773-4781, 1991). Figure 7A depicts the nucleotide sequence of an agfA gene fragment that was amplified from the S. enteritidis 27655-3b TxφhoA mutant strain and then cloned into pUC19. The bases underlined in the agfA sequence of Figure 7A are common to portions of the PCR primers TAF1 and TAF2, which were used in amplification of this fragment. Below the agfA sequence in Figure 7 A is the translated amino acid sequence. As discussed further below, the nucleotide sequences targeted by the diagnostic PCR primer pairs TAF3 and TAF4 (solid arrows) and TAF5 and TAF6 (dashed arrows) are also indicated in Figures 3A-3B. Below the agfA sequence in Figure 7 is the translated amino acid sequence. Figure 7B depicts the nucleotide and amino acid sequences of the full agfA gene of S. enteritidis 27655-3b. D. tctA. tctB. and tctC genes, and the tctl. tctll and tct/77 operons The tctA, tctB, tctC and tctD genes are located in the tct7 operon, which is one of three operons for tricarboxylic acid transport within Salmonella spp. The other Salmonella tricarboxylic acid transport systems are termed tctll and tct777. It is believed that the tricarboxylic acid transport system of Salmonella is lacking from several other related genera of Enterobacteriaceae . tctl and tct777 both encode proteins responsible for citrate transport and are induced by growth of Salmonella typhimurium on minimal media supplemented with citrate as a carbon source, tctll is normally not expressed. Each system demonstrates preferential transport of various tricarboxylic acids and different concentrations of the monovalent cations Na + and K + . The transport of tricarboxylic acids, particularly citrate, are potentially important to the intracellular survival of Salmonella, as such transport provides a means of scavenging nutrients from a host cell. Accordingly, mutants in these various tct systems, preferably in S. typhimurium or S. enteritidis, potentially create attenuated strains of Salmonella capable of being taken into a host cell, and capable of persisting for a limited time, yet not able to proliferate within such a host cell. In a preferred embodiment, one or more of these tct mutants are coupled with a mutant unable to utilize succinate to provide a "back-up" system to assure attenuation. The nucleotide sequences for tctA, tctB and tctC, along with their corresponding amino acids, are depicted in Figures 4, 5 and 6, respectively. π. Vector Constructs Comprising the Gene Sequences of the Present Invention A. Vector Constructs Generally The present invention provides for the manipulation and expression of the above described genes by culturing host cells containing a construct capable of expressing the above-described genes, including substantially similar derivatives thereof. Numerous vector constructs, including all or part of the nucleotide sequences of a native or derivative sefA, seβ, sefC, seβ, sefU2, sefUj, agfA, tctA, tctB, and/or tctC genes, as described above, can be prepared as a matter of convenience. Within the context of the present invention, a DNA construct is understood to refer to a DNA molecule, or a clone of such a molecule (either single-stranded or double- stranded), that has been modified through human intervention to contain segments of DNA combined and juxtaposed in a manner that as a whole would not otherwise exist in nature. Vector constructs of the present invention comprise a first DNA segment encoding one or more of the sefA, seβ, sefC, seβ, sefUj, sefU2, agfA, tctA, tctB, and/or tctC genes operably linked to additional DNA segments required for the expression of the first DNA segment. Within the context of the present invention, additional DNA segments will include a promoter and will generally include transcription terminators, and may further include enhancers and other elements. Mutations in nucleotide sequences constructed for expression of variant proteins preferably preserve the reading frame of the coding sequences. Furthermore, the mutations will preferably not create complementary regions that could hybridize to produce secondary mRNA structures, such as loops or hairpins, that would adversely affect translation of the mRNA. Although a mutation site may be predetermined, it is not necessary that the nature of the mutation per se be predetermined. For example, in order to select for optimum characteristics of mutants at a given site, random mutagenesis may be conducted at the target codon and the expressed mutants screened for indicative biological activity. Mutations may be introduced at particular loci by synthesizing oligonucleotides containing a mutant sequence, flanked by restriction sites enabling ligation to fragments of the native sequence. Following ligation, the resulting reconstructed sequence encodes a derivative having the desired amino acid insertion, substitution, or deletion. Alternatively, oligonucleotide-directed site-specific mutagenesis procedures may be employed to provide an altered gene having particular codons altered according to the substitution, deletion, or insertion required. Exemplary methods of making the alterations set forth above are disclosed by Walder et al. {Gene 42:133, 1986); Bauer et al. {Gene 37:13, 1985); Craik {BioTechniques, January 1985, 12-19); Smith et al. {Genetic Engineering: Principles and Methods, Plenum Press, 1981); and Sambrook et al. {supra). The primary amino acid structure of the above described proteins may also be modified by forming covalent or aggregative conjugates with other chemical moieties, such as glycosyl groups, lipids, phosphate, acetyl groups, or with other proteins or polypeptides. Within a further embodiment, the above described proteins may be fused with other peptides that facilitate purification or identification of these proteins. For example, a protein can be prepared as a fusion protein with the FLAG polypeptide sequence {see U.S. Patent No. 4,851,341; see also Hopp et al., Bio/Technology 6:1204, 1988). The FLAG polypeptide sequence is highly antigenic and provides an epitope for binding by a specific monoclonal antibody, enabling rapid purification of the expressed recombinant protein. This sequence is also specifically cleaved by bovine mucosal enterokinase at the residue immediately following the Asp-Lys pairing. B. Expression Vectors One type of vector construct, known as an expression vector, can contain DNA segments necessary to direct the secretion of a polypeptide of interest. Such DNA segments can include at least one secretory signal sequence. Preferred secretory signals include the yeast alpha factor signal sequence (pre-pro sequence; Kurjan and Herskowitz, Cell 30:933-943, 1982; Kurjan et al., U.S. Patent No. 4,546,082; Brake, EP 116,201), the Pho5 signal sequence (Beck et al., WO 86/00637), the Suc2 signal sequence (Carlson et al., Mol. Cell. Biol. 3:439-447, 1983), the α-2 plasmin inhibitor signal sequence (Tone et al., J. Biochem. (Tokyo) 702:1033-1042, 1987), the tissue plasminogen activator signal sequence (Pennica et al., N " ature 307:214-221, 1983), the E. coli PhoA signal sequence (Yuan et al., J. Biol. Chem. 265:13528-13552, 1990), or any of the other bacterial signal sequences known in the art, such as those reviewed by Oliver {Ann. Rev. Microbiol. 39:615-649, 1985). Alternatively, a secretory signal sequence can be synthesized according to the rules established, for example, by von Heinje {Eur. J. Biochem. 733:17-21, 1983; J. Mol Biol 184:99-105, 1985; Nuc. Acids Res. 74:4683-4690, 1986). Secretory signal sequences can be used singly or in combination. For expression, a DNA molecule as described above is inserted into a suitable vector construct, which in turn is used to transform or transfect appropriate host cells for expression. Host cells suitable for use in practicing the present invention include mammalian, avian, plant, insect, bacterial and fungal cells. Preferred eukaryotic cells include cultured mammalian cell lines {e.g., rodent or human cell lines) and fungal cells, including species of yeast {e.g., Saccharomyces spp., particularly S. cerevisiae, Schizosaccharomyces spp., or Kluyveromyces spp.) or filamentous fungi {e.g., Aspergillus spp., Neurospora spp.). Strains of the yeast Saccharomyces cerevisiae are particularly preferred. Methods for producing recombinant proteins in a variety of prokaryotic and eukaryotic host cells are generally known in the art {see, "Gene Expression Technology," Methods in Enzymology, Vol. 185, Goeddel (ed.), Academic Press, San Diego, Calif., 1990; see also, "Guide to Yeast Genetics and Molecular Biology," Methods in Enzymology, Guthrie and Fink (eds.), Academic Press, San Diego, Calif, 1991). In general, a host cell will be selected on the basis of its ability to produce the protein of interest at a high level or its ability to carry out at least some of the processing steps necessary for the biological activity of the protein. In this way, the number of cloned DNA sequences that must be introduced into the host cell can be minimized and overall yield of biologically active protein can be maximized. Suitable yeast vectors for use in the present invention include YRp7 (Struhl et al., Proc. Natl. Acad Sci. USA 76:1035-1039, 1978), YEpl3 (Broach et al., Gene 5:121-133, 1979), pJDB249 and pJDB219 (Beggs, Nature 275:104-108, 1978) and derivatives thereof. Such vectors will generally include a selectable marker, which may be one of any number of genes that exhibit a dominant phenotype for which a phenotypic assay exists to enable transformants to be selected. Preferred selectable markers are those that complement host cell auxotrophy, provide antibiotic resistance or enable a cell to utilize specific carbon sources, and include leu2 (Broach et al., ibid), ura3 (Botstein et al., Gene 5:17, 1979), or his3 (Struhl et al., ibid). Another suitable selectable marker is the cat gene, which confers chloramphenicol resistance on yeast cells. Preferred promoters for use in yeast include promoters from yeast glycolytic genes (Hitzeman et al., J. Biol. Chem. 255:12073-12080, 1980; Alber and Kawasaki, J. Mol. Appl. Genet. 7:419-434, 1982) or alcohol dehydrogenase genes (Young et al., in Genetic Engineering of Microorganisms for Chemicals, Hollaender et al. (eds.), p. 355, Plenum, New York, 1982; Ammerer, Meth. Enzymol. 707:192-201, 1983). The expression units may also include a transcriptional terminator. In addition to yeast, proteins of the present invention can be expressed in filamentous fungi, for example, strains of the fungi Aspergillus (McKnight et al., U.S. Patent No. 4,935,349, which is incorporated herein by reference). Examples of useful promoters include those derived from Aspergillus nidulans glycolytic genes, such as the adh3 promoter (McKnight et al., EMBO J. 4:2093-2099, 1985). An example of a suitable terminator is the adh3 terminator (McKnight et al., ibid., 1985). The expression units utilizing such components are cloned into vectors that are capable of insertion into the chromosomal DNA oϊ Aspergillus. Techniques for transforming fungi are well known in the literature, and have been described, for instance, by Beggs {ibid.), Hinnen et al. {Proc. Natl Acad Sci. USA 75:1929-1933, 1978), Yelton et al. {Proc. Natl. Acad Sci. USA 57:1740-1747, 1984), and Russell {Nature 307:167-169, 1983). The genotype of the host cell will generally contain a genetic defect that is complemented by the selectable marker present on the expression vector. Choice of a particular host and selectable marker is well within the level of ordinary skill in the art. In addition to fungal cells, cultured mammalian cells may be used as host cells within the present invention. Preferred cultured mammalian cells for use in the present invention include the COS-1 (ATCC No. CRL 1650), COS-7 (ATCC No. CRL 1651), BHK (ATCC No. CRL 1632), and 293 (ATCC No. CRL 1573; Graham et al., J. Gen. Virol. 36:59-12, 1977) cell lines. A preferred BHK cell line is the BHK 570 cell line (deposited with the American Type Culture Collection under accession number CRL 10314). In addition, a number of other mammalian cell lines may be used within the present invention, including Rat Hep I (ATCC No. CRL 1600), Rat Hep II (ATCC No. CRL 1548), TCMK (ATCC No. CCL 139), Human lung (ATCC No. CCL 75.1), Human hepatoma (ATCC No. HTB-52), Hep G2 (ATCC No. HB 8065), Mouse liver (ATCC No. CCL 29.1), NCTC 1469 (ATCC No. CCL 9.1), SP2/0-Agl4 (ATCC No. 1581), HIT-T15 (ATCC No. CRL 1777), and RINm 5AHT 2 B (Orskov and Nielson, FEBS 229(1): 175-178, 1988). Mammalian expression vectors for use in carrying out the present invention will include a promoter capable of directing the transcription of a cloned gene or cDNA. Preferred promoters include viral promoters and cellular promoters. Viral promoters include the immediate early cytomegalovirus promoter (Boshart et al., Cell 47:521-530, 1985) and the SV40 promoter (Subramani et al., Mol. Cell. Biol. 7:854- 864, 1981). Cellular promoters include the mouse metallothionein-1 promoter (Palmiter et al., U.S. Patent No. 4,579,821), a mouse V: promoter (Bergman et al., Proc. Natl. Acad Sci. USA 57:7041-7045, 1983; Grant et al., Nuc. Acids Res. 75:5496, 1987) and a mouse VJJ promoter (Loh et al., Cell 33:85-93, 1983). Such expression vectors may also contain a set of RNA splice sites located downstream from the promoter and upstream from the DNA sequence encoding the peptide or protein of interest. Preferred RNA splice sites may be obtained from adenovirus and/or immunoglobulin genes. Also contained in the expression vectors is a polyadenylation signal located downstream of the coding sequence of interest. Suitable polyadenylation signals include the early or late polyadenylation signals from SV40 (Kaufman and Sharp, ibid), the polyadenylation signal from the Adenovirus 5 E1B region and the human growth hormone gene terminator (DeNoto et al., Nuc. Acids Res. 9:3719-3730, 1981). The expression vectors may include a noncoding viral leader sequence, such as the Adenovirus 2 tripartite leader, located between the promoter and the RNA splice sites. Preferred vectors may also include enhancer sequences, such as the SV40 enhancer and the mouse 1 enhancer (Gillies, Cell 33:717-728, 1983). Expression vectors may also include sequences encoding the adenovirus VA RNAs. Suitable expression vectors can be obtained from commercial sources {e.g., Stratagene, La Jolla, Calif.). Vector constructs comprising cloned DNA sequences can be introduced into cultured mammalian cells by, for example, calcium phosphate-mediated transfection (Wigler et al., Cell 14:125, 1978; Corsaro and Pearson, Somatic Cell Genetics 7:603, 1981; Graham and Van der Eb, Virology 52:456, 1973), electroporation (Neumann et al., EMBO J. 7:841-845, 1982), or DEAE-dextran mediated transfection (Ausubel et al. (eds.), Current Protocols in Molecular Biology, John Wiley and Sons, Inc., NY, 1987), which are incorporated herein by reference. To identify cells that have stably integrated the cloned DNA a selectable marker is generally introduced into the cells along with the gene or cDNA of interest. Preferred selectable markers for use in cultured mammalian cells include genes that confer resistance to drugs, such as neomycin, hygromycin, and methotrexate. The selectable marker may be an amplifiable selectable marker. Preferred amplifiable selectable markers are the DHFR gene and the neomycin resistance gene. Selectable markers are reviewed by Thilly {Mammalian Cell Technology, Butterworth Publishers, Stoneham, M which is incorporated herein by reference). The choice of selectable markers is well within the level of ordinary skill in the art. As discussed further below, naked vector constructs can also be taken up by muscular cells subsequent to injection into the muscle of a mammal (or other animals). Selectable markers may be introduced into the cell on a separate vector at the same time as the sefA, B, sefC, seβ, agfA, tctA, tctB, and/or tctC genes sequences, or they may be introduced on the same vector. If on the same vector, the selectable marker and the sefA, seβ, sefC, seβ, agfA, tctA, tctB, and/or tctC genes sequences may be under the control of different promoters or the same promoter, the latter arrangement producing a dicistronic message. Constructs of this type are known in the art (for example, Levinson and Simonsen, U.S. Patent No. 4,713,339). It can also be advantageous to add additional DNA, known as "carrier DNA" to the mixture that is introduced into the cells. Mammalian cells containing a suitable vector are allowed to grow for a period of time, typically 1-2 days, to begin expressing the DNA sequence(s) of interest. Drug selection is then applied to select for growth of cells that are expressing the selectable marker in a stable fashion. For cells that have been transfected with an amplifiable, selectable marker the drug concentration may be increased in a stepwise maimer to select for increased copy number of the cloned sequences, thereby increasing expression levels. Cells expressing the introduced sequences are selected and screened for production of the protein of interest in the desired form or at the desired level. Cells that satisfy these criteria can then be cloned and scaled up for production. The preferred prokaryotic host cell for use in expressing the gene sequences of the present invention is Salmonella. Other preferred host cells include strains of the bacteria E. coli, although Bacillus, Shigella and other genera are also useful. Techniques for transforming these hosts and expressing foreign DNA sequences cloned therein are well known in the art {see, e.g., Maniatis et al., Molecular Cloning: A Laboratory Manual, Cold Spring Harbor Laboratory, 1982, which is incorporated herein by reference; or Sambrook et al., supra). Vectors used for expressing cloned DNA sequences in bacterial hosts will generally contain a selectable marker, such as a gene for antibiotic resistance, and a promoter that functions in the host cell. Appropriate promoters include the trp (Nichols and Yanofsky, Meth. Enzymol 707:155- 164, 1983), lac (Casadaban et l., J. Bacterial 743:971-980, 1980), and phage λ (Queen, J. Mol. Appl. Genet. 2:1-10, 1983) promoter systems. Plasmids usefiil for transforming bacteria include the pUC plasmids (Messing, Meth. Enzymol. 707:20-78, 1983; Vieira and Messing, Gene 79:259-268, 1982), pBR322 (Bolivar et al., Gene 2:95- 113, 1977), pCQV2 (Queen, ibid.), and derivatives thereof. Plasmids may contain both viral and bacterial elements. Given the teachings provided herein, promoters, terminators and methods for introducing expression vectors encoding sefA, B, sefC, seβ, agfA, tctA, tctB, and/or tctC genes of the present invention into plant, avian, fish and insect cells would be evident to those of skill in the art. The use cf baculoviruses, for example, as vectors for expressing heterologous DNA sequences in insect cells has been reviewed by Atkinson et al. {Pestic. Sci. 25:215-224,1990). In addition, the use of Agrobacterium rhizogenes as vectors for expressing genes in plant cells has been reviewed by Sinkar et al. {J. Biosci. (Bangalore) 77:47-58, 1987). Host cells containing vector constructs of the present invention are then cultured to express a DNA molecule as described above. The cells are cultured according to standard methods in a culture medium containing nutrients required for growth of the chosen host cells. A variety of suitable media are known in the art and generally include a carbon source, a nitrogen source, essential amino acids, vitamins and minerals, as well as other components, e.g., growth factors or serum, that may be required by the particular host cells. The growth medium will generally select for cells containing the DNA construct(s) by, for example, drug selection or deficiency in an essential nutrient which is complemented by the selectable marker on the DNA construct or co-transfected with the DNA construct. Suitable growth conditions for yeast cells, for example, include culturing in a chemically defined medium, comprising a nitrogen source, which may be a non- amino acid nitrogen source or a yeast extract, inorganic salts, vitamins and essential amino acid supplements at a temperature between 4°C and 37°C, with 30°C being particularly preferred. The pH of the medium is preferably maintained at a pH greater than 2 and less than 8, more preferably pH 5-6. Methods for maintaining a stable pH include buffering and constant pH control. Preferred agents for pH control include sodium hydroxide. Preferred buffering agents include succinic acid and Bis-Tris (Sigma Chemical Co., St. Louis, Mo.). Due to the tendency of yeast host cells to hyperglycosylate heterologous proteins, it may be preferable to express the sefA, B, sefC, seβ, agfA, tctA, tctB, and or tctC genes of the present invention in yeast cells having a defect in a gene required for asparagine-linked glycosylation. Such cells are preferably grown in a medium containing an osmotic stabilizer. A preferred osmotic stabilizer is sorbitol supplemented into the medium at a concentration between 0.1 M and 1.5 M, preferably at 0.5 M or 1.0 M. Cultured mammalian cells are generally cultured in commercially available serum-containing or serum-free media. Selection of a medium and growth conditions appropriate for the particular cell line used is well within the level of ordinary skill in the art. IE. Proteins A. Proteins Generally As noted above, the present invention also provides isolated proteins. Within the context of the present invention, such proteins are understood to include the whole, or portions, of a gene product derived from one or more of the sefA, seβ, sefC, seβ, agfA, tctA, tctB, and/or tctC genes, or derivatives thereof as discussed above. Where the protein is a portion of a native gene or is encoded by derivative of a native gene, the protein maintains substantially the same biological activity of the native protein. The structure of the proteins corresponding to the sefA, seβ, sefC, seβ, agfA, tctA, tctB, and/or tctC genes can be predicted from the primary translation products using the hydrophobicity plot function of, for example, P/C Gene or Intelligenetics Suite (Intelligenetics, Mountain View, Calif), or according to the methods described by Kyte and Doolittle (J. Mol. Biol. 757:105-132, 1982). B. Purification of Proteins Proteins can be isolated by, among other methods, culturing suitable host and vector systems to produce the recombinant translation products of the present invention. Supernatants from such cell lines, or protein inclusions or whole cells where the protein is not excreted into the supernatant, can then be treated by a variety of purification procedures in order to isolate the desired proteins. For example, the supernatant may be first concentrated using commercially available protein concentration filters, such as an A icon or MUlipore Pellicon ultrafiltration unit. Following concentration, the concentrate may be applied to a suitable purification matrix such as, for example, an anti-protein antibody bound to a suitable support. Alternatively, anion or cation exchange resins may be employed in order to purify the protein. As a further alternative, one or more reverse-phase high performance liquid chromatography (RP-HPLC) steps may be employed to further purify the protein. Other methods of isolating the proteins of the present invention are well known in the skill of the art. A protein is deemed to be "isolated" within the context of the present invention if no other (undesired) protein is detected pursuant to SDS-PAGE analysis followed by coomassie blue staining. Within other embodiments, the desired protein can be isolated such that no other (undesired) protein or LPS is detected pursuant to SDS- PAGE analysis followed by silver staining. IV. Compositions Capable of Eliciting an Immune Response, and Vaccines A Peptide Compositions The present invention provides isolated compositions capable of eliciting an immune response, such as immunogens, comprising the amino acid sequences shown in Figures 2 to 7B, or substantial equivalents thereof. Various portions of such amino acid sequences can also be utilized withm the context of the present invention. The immunogen may be selected from a portion of the amino acid sequences that is as small as 5 amino acids or as large as about 40 to 50 amino acids, but preferably the portion will be about 12 to 35 amino acids in length. In preferred embodiments, the immunogen comprises a GWPQ amino acid sequence or a-se D amino acid sequence. As will be understood by one of ordinary skill in the art, slight deviations of the amino acid sequences can be made without affecting the immunogenicity of the immunogen. Substantial equivalents of the above proteins include conservative substitutions of amino acids that maintain substantially the same charge and hydrophobicity as the original amino acid. Conservative substitutions include replacement of valine for isoleucine or leucine, and aspartic acid for glutamic acid, as well as other substitutions of a similar nature (See Dayhoff et al. (ed.), "Atlas of Protein Sequence and Structure," Natl. Biomed Res. Fdn., 1978). Fimbriae, preferably one or more of SEF14, SEF17, SEF18 and SEF21, when expressed on whole cell (either viable whole cells or in bacterin form) or when presented in a purified form, are capable of eliciting an immune response in animals. In addition, the proteins can be used to generate either polyclonal or monoclonal antibodies. In a prefered embodiment, the isotype of the antibodies (preferably monoclonal antibodies) is IgA Thus, the fimbriae can be an important bacterial cell component in generating host mucosal immunity to Salmonella, an enteric pathogen. As will be evident to one of ordinary skill in the art, the immunogens listed above, including their substantial equivalents, may stimulate different levels of response in different animals. The immunogens listed above, including their substantial equivalents, can be tested for effectiveness as a vaccine in experiments as described below in the Examples. These experiments include the T-cell proliferation assays, determination of lymphokine production after stimulation, and immunoprotection trials. Briefly, T-cell proliferation assays can be utilized as an indicator of potential for cell mediated immunity. Additionally, evidence of lymphokine production after stimulation by an immunogen can be utilized to determine the potential for protection provided by an immunogen. Finally, as described below, trials can be performed in order to determine the level of elicitation of an immune response, including actual immunoprotection, in animals. In the case of humans however, instead of initial immunoprotection trials it is preferred to first screen peripheral blood lymphocytes (PBLs) from patients infected with Salmonella in the following manner. Briefly, PBLs can be isolated from diluted whole blood using Ficoll density gradient centrifugation and utilized in cell proliferation studies with ^H-thymidine as described below. Positive peptides are then selected and utilized in primate trials. The immunogens or peptides of the present invention can be readily produced utilizing many techniques well known in the art {see Sambrook et al., supra, Molecular Cloning, A Laboratory Manual, Cold Spring Harbor Laboratory Press, 1989). Particularly preferred is the synthesis of the immunogens utilizing conventional peptide synthesizers. B. Attenuated Bacterial Compositions 1. Compostitions using attenuated Salmonella As discussed above, an aspect of the present invention is the induction of mutations in the tctl, tctll or tctlll operons, which are responsible for citrate transport in Salmonella. Because Salmonella containing such mutations are not able to scavenge for certain nutrients from a host cell, the Salmonella is typically unable to proliferate within a host cell. However, a Salmonella having an inoperative tricaiboxylic acid transport system is still capable of being taken into a host cell, giving an infected cell, and is able to persist within the host cell for some time, thereby allowing the Salmonella to elicit a response from the immune system of the host animal. Such a Salmonella is known as an attenuated Salmonella. In an alternative embodiment, the Salmonella is attenuated via introducing a mutation into two or more of its fimbrial genes, sefA, seβ, agfA, and flmA, wherein the mutation effectively prevents production of the selected fimbriae by the Salmonella. In preferred embodiments, the mutations are induced in the fimA gene {SEF21) and the agfA gene (SEF17). In an alternative preferred embodiment, the mutations are induced in the fimA (SEF21), agfA gene (SEF17) and seβ gene (SEF18). Further, where S. enteritidis is a concern, the group of mutations will preferably include a mutation in the sefA gene (SEF14). Alternatively, because SefA protein and SEF14 fimbriae are known to induce a T-cell response, the group of mutations may also include a mutation in sefA that permits production of SEF14 but disrupts any toxic effect that may be due to SEF14. Preferably, such a mutation in sefA is caused by inserting a foreign nucleic acid molecule in an appropriate portion of the sefA gene. Other mutations that provide an attenuated Salmonella are also known and, while not prefered, can be useful within some aspects of the present invention. Examples of such attenuating mutations include the following: galE mutants, which lack UDP galactose epimerase (such mutants also reversibly lack LPS and the Vi antigen) (Nnalue and Stocker, Microb. Path. 7:299-310, 1989; Germanier and Rurer, J. Infect. Dis. 737:553-558, 1975); aroA or L→aroA mutants, which are blocked in aromatic amino acid biosynthesis, as well as other aro genes including aroC and aroD (Hoiseth and Stocker, Nature 797:238-239, 1981; Dougan et al., Molec. Gen. Genet. 207:402- 405, 1987; Brown et al., J. Infect. Dis. 755:86-92, 1987); Jones et al., Vaccine 9:29-34, 1991; Mukkur et al., J. Med Microbiol 34:51-62, 1991; Robertsson et al., Infect. Immun. 41:142-150, 1983; Cooper et al., Microb. Pathog. 9:255-265, 1990); AcyaAcψ combined deletion mutants, which lack adenylate cyclase and cAMP receptor protein (Curtiss and Kelly, Infect. Immun. 5:3035, 1987); AphoP mutants, which lack the regulatory gene involved in acid phosphatase production: (Galan and Curtiss. Microb. Path. 6:433, 1989; Miller et al. Res. Microbiol. 141:817, 1990); purA or Δpur purine biosynthesis mutations, which are typically not useful alone, but rather when used in combination with aroA and galE (Nnalue and Stocker, Infect. Immun. 55:955, 1987; Sigward et al., Infect. Immun. 57:1858-1861, 1989); Δcdt mutants, which have a mutation of the chromosome that blocks Salmonella from colonizing deep tissue (Curtiss et al., Vet. Microbiol. 37:397-405, 1993); phoP^ mutants, which are constitutive producers of phoP (Miller and Mekalanos, J. Bacteriol 772:2485-2490, 1990.); streptomycin independent reverse mutants (Pardon, Res. Microbiol. 141:945- 953, 1990); attachment invasion deficient mutants of S. choleraesuis (Wilson et al., Res. Microbiol 7^7:827-830, 1990); temperature-sensitive S. enteritidis mutants (Onozuka et al., Int J. Immunopharm. 77:781-787, 1989); his mutants in combination with L→aroA and Δpur mutants (Edwards and Stocker., J. Bacteriol. 170:3991-3991, 1989); Asp", Hst, Rbt, Rtt (asparagdne auxotroph, high sensitivity to tensides, reversion to feile tolerance, reversion to tenside tolerance) mutants, which have various mutations that are useful to generate strains with graded attenuation: (Linde et al., Vaccine 5:278-282, 1990); htrA mutants, which lack a stress protein serine protease: (Strahan et al., Microb. Path. 12:311-317, 1992); and, mutants that lack the virulence plasmid (Naka ura et al., Infect. Immun. 50:586, 1985; Barrow, 7w/ect. Immun. 58:2283, 1990) In preferred embodiments, the host animal is a fish or a warm-blooded animal, and further preferably is a food animal such as poultry, swine or cattle, or even further preferably a human being. In a preferred embodiment, the attenuated Salmonella have been engineered to express a foreign gene (including portions thereof) fused to one or more genes that code for the fimbrin proteins SefA, SefD or AgfA. In a preferred embodiment, the fusion protein comprises a portion of the SEF17 fimbrin, which is encoded by the agfA gene operably linked in open reading frame to the gene for the foreign antigen. In an alternative preferred embodiment, the fusion protein comprises a portion of the SEF14 fimbrin, encoded by the sefA gene, the SEF18 fimbrin, encoded by the seβ gene, or the SEF21 fimbrin, encoded by t e fimA gene. By "foreign antigen" it is meant an antigen foreign to the host cell and not typically expressed in a Salmonella fimbriae. Preferably, the foreign antigen is foreign to both the host cell and the Salmonella. The "foreign antigen" includes a whole antigen, as well as a portion of an antigen, comprising numerous epitopes, and also includes an antigen, or portion of an antigen, that is a single epitope. In a preferred embodiment, the attenuated Salmonella composition, including an attenuated Salmonella composition comprising a foreign antigen, is an LPS O-polysaccharide deficient strain of Salmonella able to express SEF18 or SEF17 fimbriae (which include the foreign antigen, where such is present). In alternative embodiments, the fusion proteins are not expressed as fimbriae, but rather as protein aggregates, inclusion bodies or stable polymers of AgfA, SefA, SefD, SefC, SefB, TctC, TctB or TctA In a further alternative embodiment, the fusion protein comprises more than one foreign antigen. 2. COMPOSITIONS USING ATTENUATED E. con In an alternative embodiment, the attenuated bacteria can be an attenuated E. coli able to express one or more Salmonella sefA, seβ, sefC, seβ, agfA, tctC, tctB or tctA fimbriae genes. In a preferred embodiment, the expressed gene is the agfA gene. In alternative preferred embodiments, the expressed gene is the sefA gene, the seβ gene, or the fimA gene. In an alternative embodiment, the peptide corresponding to the desired gene is not displayed as an intact fimbriae, but is still able to elicit an immune response from the host organism. In preferred embodiments, the host animal is a fish or a warm-blooded animal, and further preferably is a food animal such as poultry, swine or cattle. Further preferably, the host animal is a human being. In a preferred embodiment, the E. coli or other bacterial host cell expresses a Salmonella AgfA, FimA SefA SefD, SefC, SefB, TctC, TctB or TctA protein fused to one or more foreign antigens. The Salmonella protein is further preferably a fimbrin protein, further preferably SefA, AgfA, SefD or FimA. Further, preferably both the Salmonella-based antigen and the foreign antigen are able to elicit a response from the immune system of the host animal, yielding a multipurpose composition/immunogen. C. Nucleic Acid Vaccines 1. Generally Direct injection, or other appropriate introduction, of one or more of the sefU2, sefUj, sefA, seβ, seβ, seβ tctC, tctB, tctA, or αgfA genes into an animal can elicit an immune response in the animal, and preferably vaccinate, against the peptide that is expressed from the given gene, and therefore Salmonella. In one embodiment, the nucleic acid that is injected further comprises an antigen from a foreign microbe, thereby providing a composition able to elicit an immune response against microbes in addition to Salmonella. In an example of this procedure, naked DNA is introduced into an appropriate cell, such as a muscle cell, where it produces protein that is then displayed on the surface of the cell, thereby eliciting a response from host cytotoxic T- lymphocytes (CTLs). This provides an advantage over traditional immunogens wherein the elicited response comprises specific antibodies. Specific antibodies are generally strain-specific and cannot recognize the corresponding antigen on a different strain. CTLs, on the other hand, are specific for conserved antigens and can respond to different strains expressing a corresponding antigen ("Heterologous protection against influenza by injection of DNA encoding a viral protein," Ulmer et al., Science 259:1745- 1749 (1993); "Expression of recombinant genes in myocardium in vivo after direct injection of DNA" Lin et al., Circulation 82:2211-21 (1990); "Long-term persistence of plasma DNA and foreign gene expression in mouse muscle," Wolff et al., Human Mol Gen. 7:363-69 (1992)). In preferred embodiments, the vector construct containing one or more of the gene sequences of the present invention is naked and is injected into a muscle of an animal, resulting in the uptake of the vector construct by the muscle cells of the animal, and expression of the protein encoded by the DNA. In preferred embodiments, the vector construct is injected into fish or warm-blooded animals, including birds, mice, rats, primates and human beings. Further, it is preferred that the vector construct is a DNA expression vector wherein the desired gene is under the control of a Rous sarcoma virus (RSV) or cytomegalo virus (CMV) promoter (Ulmer et al., supra; Lin et al.). Further preferably, the plasmid resists incorporation into the chromosomal DNA of the animal's cell, and does not replicate within the animal's cell (Wolff et al., supra). Upon introduction of the naked vector construct into the animal's cell, the construct is then able to express the gene that it carries, which gene preferably comprises one (or more) of the sefUj, sefU2, sefA, seβ, seβ, seβ, tctC, tctB, tctA, or agfA genes. Accordingly, upon expression of the desired peptide, an immune response is elicited from the host animal. Preferably, the immune response includes CD8 + CTLs able to respond to different strains that exhibit a form of the desired peptide. In another preferred embodiment, one of the desired proteins discussed above is operably fused in an open reading frame to a second nucleotide sequence (or more) that codes for a foreign antigen, to yield a single dicistronic protein exhibiting antigenic characteristics of both Salmonella and another, foreign organism. D. Administration of Compositions Able to Elicit an Immune Response 1. Peptide Compositions The present invention provides methods for simulating an immune response in warm-blooded animals comprising administering an effective amount of a pharmaceutical composition comprising an immunogen and a physiologically acceptable carrier or diluent. For purposes of the present invention, warm-blooded animals include, among others, humans, primates, dogs, cats, pigs, sheep, horses, rats, mice, chickens, turkeys and other food animals. The methods can also be used for stimulating an immune response in cold-blooded animals, preferably food animals such as fish. Many suitable carriers or diluents can be utilized in the present invention, including among others saline, buffered saline, and saline mixed with nonspecific serum albumin. The pharmaceutical composition may also contain other excipient ingredients, including adjuvants, buffers, antioxidants, carbohydrates such as glucose, sucrose, or dextrins, and chelating agents such as EDTA. Within a particularly preferred embodiment, an adjuvant is utilized along with the immunogen. Examples of such adjuvants include alum or aluminum hydroxide for humans. The amount and frequency of administration can be determined in clinical trials, and will depend upon such factors as the Salmonella species against which it is desired to protect, the particular immunogen used, the degree of protection required, and many other factors. In a preferred embodiment, the composition is administered orally, and the attenuated Salmonella are taken up by cells, such as cells located in the lumen of the gut. Alternatively, the composition can be parenterally administrated via the subcutaneous route, or via other routes. Depending upon the application, quantities of injected immunogen will vary from 50 μg to several milligrams in an adjuvant vehicle and preferably about 100 μg to 1 mg, in combination with a physiologically acceptable carrier or diluent. Booster immunizations can be given from 4-6 weeks later. 2. Attenuated Bacterial Compositions Attenuated bacterial compositions are preferably administered orally in combination with a physiologically acceptable carrier or diluent. However, attenuated bacterial compositions can also be administered via the same mechanisms as peptide- based compositions, such as via injection in combination with an adjuvant. The following Examples are offered by way of illustration, and not by way of limitation. EXAMPLES EXAMPLE 1 Cloning of the agfA gene of Salmonella enteritidis An AgfA-negative ΥxφhoA insertion mutant of S. enteritidis 27655-3b, named strain 2-7-ζ was constructed (Collinson et al., "Thin, aggregative fimbriae mediate binding of Salmonella enteritidis to fibronectin," J. Bacteriol 775:12-18, 1993). The strain contains an agfA-TaphoA gene fusion. Stock cultures of strain 2-7f were prepared using cells from mid-exponential phase cultures that were mixed with 7% glycerol and then stored at -80°C in Luria-Bertani (LB) broth. Isolated colonies of strain 2-7f were obtained by inoculation of solid LB medium followed by incubation at 37°C for 24 hours. An individual colony was inoculated in 2 ml of LB broth contained in a sterile 18 mm x 150 mm test tube and the inoculation was incubated for 48 hours at 37°C under static conditions. For the purpose of isolation of DNA for amplification of agfA, cells may be equally effectively prepared by growth in LB broth, Colonization Factor Antigen (CFA) broth, T (tryptone)-medium, other suitable proteolytic digest- based medium, or other medium suitable to support the growth of Salmonella. Cells may also be grown under aeration, such as by growth of the culture in an Erlenmeyer or other flask positioned on a rotary or gyratory shaking device. Preferably, the culture is grown at temperatures between 20°C and 37°C. Cells of strain 2-7f composing the pellicle at the surface of a static culture and cells in suspension were mixed by vortexing for 1 minute. Cells were harvested from 1 ml of this cell suspension (approximately 20 mg wet weight of cells) transferred to a 1.5 ml polypropylene microfuge tube and centrifuged (16,000 x g for 5 min. at 21° C). The pelleted cells were saved and subsequently resuspended in 1 ml of distilled water. The cells were lysed to release cellular DNA by boiling the 1 ml sample in a sealed microfuge tube for 5 minutes. The cell lysate was partially clarified by centrifugation (16,000 x g for 10 min. at 4°C) in a microfuge to pellet cell debris. The crude DNA preparation (supernatant fraction) was used as a substrate for amplification of a 394 bp DNA fragment encoding the majority of the SEF17 fimbrin subunit, agfA. Standard molecular cloning techniques were performed according to protocols described by Sambrook et al. {Molecular Cloning: A Laboratory Manual, Cold Spring Harbor Press, Cold Spring Harbor, New York, 1989), or by incorporating minor modifications thereto that are well known in the art. To facilitate cloning of an amplified agfA fragment, PCR primers were constructed to include restriction endonuclease cleavage sites. The 5' PCR primer, called TAF1, was a 34 bp biased, degenerate oligonucleotide dGGCGGAAGCTTGAATTCGTfA/C/TlGTfA/C/TIC C[A/G/T]CA[A/G]TGGGG) (SEQ ID No. ), of which the 17 bases at the 3' end correspond to amino acid residues 2 to 7 of the AgfA N-terminus (the final nucleotide of amino acid 7 is degenerate, and therefore was not made a part of the primer). The amino acid sequence of the N-terminus had been previously determined by Collinson et al. (supra). The underlined sequences were required to create HindJH and EcoRI cleavage sites in the product of DNA amplification. The 3' PCR primer, called TAF2, (dGGGAAAGGTTGAATTCAGGACGCTACTTGTG) (SEQ ID No. ), into which three nucleotide changes (underlined) were introduced to create an EcoRI site in the PCR product, was complementary to the IS50 L sequence residing at the junction of TτφhoA generated alkaline phosphatase gene fusions. The amplified 394 bp agfA fragment was isolated after agarose (1.5%) gel electrophoresis using a 40 mM Tris- acetate, 1 mM ΕDTA buffer system and then purified using Gene Clean II glassmilk following the 'double Gene Clean' protocol recommended by the manufacturer (Bio 101 Inc., La Jolla, CA). Approximately 0.5 μg of the amplified agfA fragment was cleaved with the restriction endonuclease EcoRI at a concentration of 5 units per μg of DNA. In addition, 0.5 μg of the plasmid vector pUC19 (Yannisch-Perron et al., "Improved M13 phage cloning vectors and host strains: nucleotide sequences of the M13mpl8 and pUC19 vectors," Gene 33:103-119, 1985) was similarly digested with EcoRI. After digestion, the DNA samples were extracted once with 0.75 volume of buffered-phenol and then with 0.75 volume of chloroform to separate enzyme from DNA. The digested DNA fragments were precipitated in the presence of 2.5 volumes of 95% ethanol and 0.3 M sodium acetate, pH 5.4. Residual ethanol was removed from the DNA pellets under vacuum. The DNA was dissolved in 20 μl of 10 mM TrisHCl - 1 mM EDTA, pH 8.0. Ligation of agfA DNA fragments into pUC19 was conducted in 50 μl ligation buffer using 7 units of T4 DNA ligase. Clones containing recombinant plasmids were obtained by transformation of competent cells of Escherichia coli strain DH5α obtained from GIBCO BRL Life Technologies Inc. (Burlington, Ontario, Canada) with a sample of ligated DNA. Transformed cells were selected on solid LB medium containing (200 μg ml) ampicillin, 50 μM IPTG (isopropyl-β-D-thiogalactopyranoside) and 0.005% X- GAL (5-bromo-4-chloro-3-indoyl-β-D-galactoside). Ampicillin resistant colonies that contained the recombinant plasmids were identified by their white color. Recombinant plasmid DNA was purified from transformed cells using a modification of the standard, small scale, alkaline lysis technique described by Sambrook et al. {supra). Recombinant plasmids were purified from three individually isolated colonies. These three, apparently identical, plasmids were designated pAGFl, pAGF3 and pAGF4. In order to obtain a clone containing the full agfA gene, chromosomal DNA of S. enteritidis strain 27655-3b was purified by CsCl gradient centrifugation and digested separately with Hzwdiπ or Dral and analyzed by Southern hybridization at 65°C using a random-primer, [α- 32 P]dATP labeled agfA PCR fragment according to methods described by Sambrook et al. {supra). Following stringent filter washing at 60° C to 62°C as described above, a genomic fragment of approximately 3 kb was identified. HindUJ or 7 αl digested strain 3b DNA was fractionated according to size by sucrose gradient centrifugation (Sambrook et al., supra). DNA fragments contained in the fraction found to hybridize to the [ 32 P]-labeled agfA PCR fragment were ligated into M13mpl8 (Yannisch-Perron et al., supra) at the Hinά→Jl site or S al site within the multiple cloning site at 12°C using 12 units of ligase and a total of 1 μg of DNA at a final concentration of 50 μg/μl. Recombinant plaques prepared on a lawn of E. coli JM109 (Yannisch-Perron et al., supra), containing agfA were identified by dot blot hybridization (Sambrook et al., supra) using the [ 32 P]-labeled agfA PCR fragment. The recombinant M13mpl8 bacteriophage containing agfA were plaque purified in the replicative form, double-stranded DNA was purified and the insert fragments encoding agfA were cloned into pUC18 (Yannisch-Perron et al., supra), and transformed into E. coli strain DH5α as described by Sambrook et al. {supra). The recombinant plasmid composed of pUC18 and the approximately 3kb Dral fragment of strain 3b DNA was named pDAG6. The recombinant plasmid formed from pUC18 and the approximately 3kb Hindm fragment of strain 3b genomic DNA was named pHAGlO. EXAMPLE 2 Determination of the DNA sequence of agfA The DNA sequences of both strands of the agfA PCR fragment of Example 1 were determined by a modification of the enzymatic, dideoxy-termination sequencing method (Sanger et al., "DNA sequencing with chain-termination inhibitors," Proc. Natl. Acad Sci. USA 74:5463-5461, 1977) using the primers TAF1 and TAF2 and the reagents and protocols supplied in the Sequenase™ Version 2.0 kit (United States Biochemicals, Cleveland, Ohio). The sequence was confirmed by determining the DNA sequence of agfA contained in two of the independent plasmid clones. For this determination, an Applied Biosystems model 373 A automated DNA sequencer and associated reagents, protocols and software (version 1.10) for thermal cycle sequencing (Applied Biosystems Canada Inc., Mississauga, ON) was used. The universal forward and reverse sequencing primers (Yannisch-Perron et al., supra) were used. The DNA sequence of agfA encoded on the overlapping HindΩ and Dral fragments cloned in pHAGlO and pDAG6 was determined on both strands using double-strand DNA sequencing techniques. Computer analysis of the DNA sequence for open reading frames and gene translation was performed using DNA Strider, version 1.1. The start of the open reading frame of the agfA gene encoding the mature AgfA fimbrin was recognized by comparison of the translated sequence to the N-terminal amino acid sequence of AgfA. The agfA DNA sequence is presented in Figure 7B. The translated DNA sequence of the single open reading frame corresponded precisely to amino acid residues 2 to 31 determined by N-terminal sequencing of AgfA. The amino acid composition of the translated sequence had a similar high glycine content (16%), high combined alanine, serine plus glycine content (37%), low basic amino acid content (4.5%), and nearly 30% asparagine plus aspartic acid content consistent with the total amino acid analysis of native AgfA fimbrin (8). Based on the estimated molecular weight of AgfA of 17 K M τ , and the expected molecular weight of the protein encoded in the 333 bp region of agfA, about 12 K - 13 K M-, it appears that about three quarters of SEF17 fimbrin is represented in the fragment. EXAMPLE 3 Production and expression of assembled. enzymatically active AefA-enzyme fusion proteins in Salmonella enteritidis Salmonella enteritidis produce novel thin aggregative fimbriae, known as SEF17, that comprise a class of stable protein polymers requiring treatment with 90% formic acid to depolymerize the fimbriae into their composite fimbrin subunits (Collinson, supra). SEF17-negative TτφhoA mutants were isolated that were defective in the production of SEF17 fimbriae due to transposon mutagenesis resulting in the fusion of the SEF17 fimbrin gene, agfA, with the promoterless alkaline phosphatase gene, phoA (Collinson et al., "Thin, aggregative fimbriae mediate binding of Salmonella enteritidis to fibronectin," J. Bacteriol 75:12-18, 1993). Western blot data indicated that the AgfA-PhoA fusion protein expressed by the TτφhoA mutant 2-7f either aggregates or self assembles into polymers because formic acid treatment was required to disassemble these polymers into the AgfA-PhoA subunits. EXAMPLE 4 Sequencing of the tctCBA gene cluster of Salmonella typhimurium The tricarboxylic acid transport {tctl) operon of Salmonella typhimurium LT2 was isolated on an 8 kb Eco→?*l-BamΗL fragment cloned into the vector pBR322 to create the recombinant plasmid pKWIOl which conferred a citrate-utilizing {cit+) phenotype on E. coli MC4100 (Widenhorn et al., "Cloning and promoters of the Salmonella typhimurium tricarboxylate transport operon in Escherichia coli," J. Bacteriol. 770:883-888, 1988). pKWIOl was digested with the restriction enzymes Kpril and Pstl to yield a fragment of 4.5 kb, containing the entire tctl operon, which was inserted into the Ml 3 cloning vector M13mpl8 (Yannisch-Perron et al., supra) to produce the recombinant clone KS1016. KS1016 was digested with the restriction enzymes EcoRI and HindUI (which cut only in the vector DNA) to release the tctl fragment for subcloning into the Ml 3 cloning vector MWB2349 to produce MKS3. (Barnes et al., "Kilo-Sequencing: Creation of an Ordered Nest of Asymmetric Deletions Across a Large Target Sequence Carried on Phage M13," Meth. Enz. 707:98-122, 1983.) To facilitate determining the DNA sequence of tctCBA, the 4.5 kb EcoRI-H dlll tct7 fragment was subcloned from KS1016 into the Ml 3 cloning vector MWB2341, whose multiple cloning site is oriented in the opposite direction relative to the binding site of the universal DNA sequencing primer. This resulted in the creation of MKS11. The recombinant clones MKS3 and MKS11 were subjected to a procedure generating nested deletions (Dale et al., "A rapid single-stranded cloning strategy for producing a sequential series of overlapping clones for use in DNA sequencing: Application to sequencing the corn mitochondrial 18S rDNA," Plasmid 73:31-40, 1985). Briefly, single-stranded recombinant M13 DNA was isolated by standard procedures (Sambrook et al., supra). DNA was linearized by HindlU digestion following hybridization of the oligonucleotide WK-10, 5'-TGAATTAATTCCA CAAGCTTTTTTTTTTT-3'; to MKS3 (SEQ ID No. ) or WK-9, 5'- CGACGGCCAGTGCCAAGCTTTTTTTTTT-3' to MKS11 (SEQ ID No. ) to create a double stranded restriction endonuclease cleavage site in an otherwise single- stranded molecule. The linearized DNA was subsequently degraded by the 3' to 5' exonuclease activity of T4 DNA polymerase. Samples were withdrawn at 15, 30, 45, 60, 75, 90 and 105 minutes. The polymerase was inactivated by treating the sample at 65°C for 2 minutes and the samples stored on ice. By withdrawing samples at different times, populations of DNA fragments with differing degrees of deletion were created. All time-point samples were pooled and the DNA was treated with terminal transferase in the presence of ATP to create a polyA tail. The deleted DNA molecules were hybridized with oligonucleotide WK-10 by heating to 65°C for 5 minutes, followed by slow cooling for 30 minutes, then ligated by T4 DNA ligase for 1 hour at 21°C and overnight at 4°C. The ligated fragments were transformed into E. coli WB373 made competent by the procedure of Mandel (Mandel and Higa, "Calcium dependent bacteriophage DNA infection," J. Mol Biol. 53:159, 1970). Well-isolated M13 plaques were picked, and grown up overnight (Sambrook et al., supra) into 2X-YT broth. The size of each recombinant DNA molecule was estimated by agarose gel electrophoresis. From over 100 plaques analyzed, 35 recombinant phage representing deletions of 0.3 - 4.8 kb were selected for DNA sequence analysis. DNA sequences were determined using standard modifications of the enzymatic dideoxy termination method of Sanger et al. {supra). To resolve the sequence of regions that proved difficult to determine by standard protocols, the sequencing reactions were performed using Sequenase (a chemically modified form of T7 DNA polymerase; US Biochemicals) and either deoxyinosine or 7- deazadeoxyguanosine in place of deoxyguanosine or standard protocol sequencing reactions were analyzed by wedge-gel electrophoresis. Whereas, most sequencing reactions utilized the universal forward sequencing primer, specific internal primers were also used. The names and sequences of the internal primers used are: WWK-19 5'- GGGCGACTATCGCGTTA-3', WWK-20 5'-AGCCACTTGTAGCGGCC-3', WWK-21 5'-GGAAGTGCATTTTACGT-3', WWK-22 5'-CATGCTGCCAAGACAGG-3', WWK- 23 5'-CTTTGGATCTGCCAGGC-3', WWK-24 5'-GCGCCGTCATGATCGCC-3' (SEQ ID Nos. , , , , , and , respectively). The sequences for tctA, tctB and tctC are shown in Figures 4A-4B, 5 and 6A-6B, respectively. The sequences of tctA, tctB, and tctC were confirmed by automated DNA sequencing using an Applied Biosystems, Inc. Model 373A automated DNA sequencer and the reagents and protocols provided by the manufacturer for cycle- sequencing (Applied Biosystems, Inc., Foster City, CA). DNA oligonucleotide sequencing primers used for this purpose included: S'TCGGGATGCTGTTCGGCG 3 ' (SEQ. ID. No. ) 5 'CTGCCTGCGGAGTCGGC 3 ' (SEQ. ID. No. ) S'GTCGCAAGGCCAAGACCG 3 ' (SEQ. ID. No. ) S'GTGTATCGGCACCACCCTG 3 ' (SEQ. ID. No. ) S'CCCGGCGATGTTCACCG 3 ' (SEQ. ID. No. ) S'CCAATACCGCGCCGGAG 3 ' (SEQ. ID. No. ) 5'GCGGAGGCAATGATGAGCG 3 ' (SEQ. ID. No. ) 5 GCCGCCATACTCACAGCC 3 ' (SEQ. ID. No. ) S'TCTTGGCAGCATGATGGCG 3 ' (SEQ. ID. No. ) S'CTGGCAATGGTCGCCCG 3 ' (SEQ. ID. No. ) 5 'GCAATCAGCAGCGCAGC 3 ' (SEQ. ID. No. ) A restriction map prepared from the DNA sequence appears in Figure 9. The Figure shows the positions of endonuclease cleavage sites for Apal, Avail, BglR, Bgll, BstU, Dral, EcoRV, Kpnl, Ncol, Sail, Smal, Sna l, Sspl and Xmnl relative to the open reading frames of tctC, tctB and tctC. DNA sequences encoding TctC were recognized by comparison to the complete sequence of TctC protein; the predicted amino acid sequence agreed with the amino acid sequence determined by peptide sequencing studies on the purified protein. The predicted size of the TctB protein based on the nucleotide sequence agreed with the size of an expressed protein as determined by SDS-PAGΕ. EXAMPLE 5 Salmonella strains containing mutations in tricarboxylate transport (tct) operons A. Construction of tct7 mutants in S. enteritidis DNA encoding the Salmonella typhimurium tctl operon was cloned into pKW108 ("Expression of the divergent tricarboxylate transport operon {tctl) of Salmonella typhimurium, " J. Bacteriol. 170:3223-3221, 1988). The DNA was cleaved with the restriction enzyme BglU, which cleaves the operon at a single site in the tctC gene. The linearized DNA was then digested with exonuclease HI and nuclease SI. Samples were withdrawn at selected time points routine in the art and the enzymatic activity was stopped by the addition of EDTA After all of the samples had been removed, the DNA was pooled, purified, then treated with the Klenow fragment of E. coli DNA polymerase I. The DNA was ligated with T4 ligase to give vector constructs that were then transformed into E. coli DH5α (Sambrook et al., supra). The resultant transformants were grown up in L-broth supplemented with 100 μg/ml ampicillin overnight and a plasmid preparation was performed by the alkaline lysis procedure (Sambrook et al., supra). The population of plasmids was sized on an agarose gel, and shown to consist of molecules of heterogeneous sizes. The plasmid DNA was pooled, then linearized with EcoRI and used to electrotransform S. enteritidis. The transformants were grown on solid modified Davis minimal medium containing 50 μg ml fluorocitrate (Fc), to select for transformants that had integrated an inactive tct7 operon into the cellular chromosome and thus were resistant to the toxic citrate analog fluorocitrate. Recombinants were screened by colony lifts followed by hybridization to probe complementary to the region that had been deleted. Colonies that hybridized poorly to the probe were picked and grown in L-broth overnight. The tctC gene was characterized by PCR using oligonucleotides complementary to the DNA sequence of nucleotides 1459-1481 and 1955-1977 of the tct7 operon {see Figures 6A-6B). One of the transformants tested showed an internal deletion in the tctC gene of approximately 300 nucleotides between 1459 and 1977. This bacteria was named S. enteritidis strain SL54. B. Construction of tctll" strain Constitutive "on" mutants of the tct77 operon in wild-type Salmonella typhimurium SU453 were isolated by plating out cells on Modified Davis Minimal Medium containing 93.4 mM Na + , with cis-aconitate as the carbon source and no K + ions (Na-cac medium). The resultant tctll° n mutants were named KS823-832. KS823 was used as a recipient strain for P22 int3 HT12/4 transducing phage (B. Ely et al., "Some improved methods in P22 transduction," Genetics 76:625-631, 1974) that had been grown on an S. typhimurium strain carrying a tct7 operon that had been insertionally activated by TnlO, which carries a tetracycline resistance gene (N. Kleckner, "Transposon TnlO Mobile genetic elements," pp. 261-298, Academic Press, N.Y., 1983). Bacteria that were tctl' and tct77° n were selected for by growth on Na-cac medium in the presence of tetracycline. The tetracycline resistant strains resulting from this cross were called KS838-847. KS838 was determined to be sensitive to fluorocitrate (Fc). KS838 was grown in the presence of Fc on Na-cac medium, using the disk radial streak assay (Somers et al., "Fluorocitrate-resistant tricarboxylate transport mutants of Salmonella typhimurium," Mol. Gen. Genet. 757:338-345), and mutants resistant to Fc (Fc R ) were collected. These resistant strains were considered tctll', and were named KS858-867. Next, the tetracycline resistance of the mobile genetic element TnlO was removed by making KS858 a recipient strain for P22 transducing phage that had been grown on wild-type Salmonella SU453. These phage replace the tct7-locus with the wild-type locus, tctl isolates were selected by growing on Davis Modified Minimal Medium supplemented with 20 mM isocitrate as a carbon source. The resultant strains were called KS950-959 and KS970-979, and are phenotypically tctl*, tctll; tctlll . These strains contain no foreign DNA or introduced antibiotic resistance genes. C. Construction of tctlll' mutants Salmonella typhimurium SU453 strains were used, through TnlO insertion, to produce a series of tctlll' isolates named S. typhimurium KS1170 and KS1169. The TnlO elements can be induced to excise through culturing the bacteria on medium containing fusaric acid (S. Maloy et al., "Selection for loss of tetracycline resistance by Escherichia coli," J. Bacteriol. 140:291-300, 1981). Several strains will suffer a deletion of tct777 flanking sequences concurrent with imprecise TnlO excision and then will be useful as attenuated strains. EXAMPLE 6 Sequencing and characterization of sefUjUiABCD from the sef operon of Salmonella enteritidis A 5.3 kb Hindlll fragment carrying the SEF 14 fimbrin structural gene and part of the sef operon was subcloned from cos48, a recombinant cosmid carrying 44 kb of S. enteritidis chromosomal DNA into pTZ19R to generate pKXl (Feutrier et al., "Cloning and expression of 'a Salmonella enteritidis fimbrin gene in Escherichia coli," J. Bacteriol. 770:4216-4222, 1988; Mϋller et al., "Fimbriation genes of Salmonella enteritidis " J. Bacteriol. 777:4648-4654, 1989). A series of overlapping deletion subclones of pKXl (ΔpKXl) were generated using pKXl linearized with EcoRI and varying degrees of DNAse I digestion according to the method of Lin et al. ("An improved DNA sequencing strategy," Anal. Biochem. 7^7:114-119, 1985), to create a collection of 50 nested deletions. The resulting linear ΔpKXl subclones were treated with the Klenow fragment of DNA polymerase I and then blunt end ligated with T4 DNA ligase to recircularize the plasmids. The various ΔpKXl were transformed into E. coli XL-1 Blue (Stratagene, La Jolla, CA) using standard procedures (Sambrook et al., supra). The ΔpKXl were purified by standard alkaline lysis procedures (Sambrook et al., supra) and run on a 1% agarose gel. A series of ΔpKXl subclones separated by about 200 to 400 bp in size were chosen and named delAlO, delB15, delB23, delCl, delD5, delD8, delD9, delDlό, delD19, delΕl, and delΕ21. Large amounts of these plasmids were purified by alkaline lysis for DNA sequencing. The ΔpKXl subclones were sequenced by the dideoxynucleotide chain termination method (Sanger et al., "DNA sequencing with chain terminating inhibitors," Proc. Natl. Acad Sci. USA 74:5463-5461, 1977) using T7 DNA polymerase (T7 DNA Polymerase Sequencing Core System, Deaza, Promega, Madison, WI) and deoxyadenosine 5'-[α-35S] triphosphate, (New England Nuclear, Markham, ON) according to the manufacturers' specifications. The result of DNA sequencing reactions were electrophoresed through a 6% polyacrylamide gel (45 W, 55-60°C) using a discontinuous buffer system (Carninci et al., "A simple discontinuous buffer system for increased resolution and speed in gel electrophoretic analysis of DNA sequence," Nucleic Acid Res. 18:204, 1989). Following electrophoresis, the gels were fixed in a solution of 12% methanol and 10% acetic acid for 15 min, and dried onto 3MM paper (Whatman Intl. Ltd., Maidstone, England) under vacuum at 80°C for 2 hours on a Savant gel drying apparatus (Savant Instruments Inc., Farmingdale, NY). Dried gels were exposed to X-Omat K XK-1 film (Kodak, Rochester, NY) and the sequence read directly from the developed films. Both DNA strands were fully sequenced, using the 17 bp reverse primer for the coding strand (GTCATAGCTGTTTCCCG) (Sequence ID No. ) and 12 custom made internal oligonucleotide primers (ULTRA Diagnostics Corporation, Seattle, WA) for the opposite strand. To complete the sequence for the seβ gene, and to sequence the sefUj and sefU2 genes, a further 10 kb Kpnl fragment was obtained from cos48 and subjected to sequence analysis generally as above. The sefA, seβ, seβ and seβ sequences are depicted in Figures 2A-2D. The genes for sefUj and sefU2 were similarly sequenced on overlapping subclones and these sequences are depicted in Figures 3A-3B. The programs contained in Mac Vector (Intelligenetics, Mountain View, CA) were used to determine the order of the overlapping DNA sequences. DNA Strider™ version 1.1 was used to identify the open reading frames for sefA, seβ and sefC, which were predicted to encode polypeptides of 14,436 Mr, 28,012 r and 90,268 Mr, respectively. The predicted amino acid sequences of the SefA SefB and SefC proteins were compared to proteins listed in the GenBank (release #66.0), SWISS- PROT (release #16.0), and GENPEPT (release #64.3) data bases and the MACAW program (NCBI, Bethesda, MD) to align regions of local similarity among proteins exhibiting similarity. The adjacent downstream gene, seβ, encodes a fimbrial periplasmic chaperone protein. seβ, the gene immediately downstream of seβ, encodes a fimbrial outer membrane protein that contains nine putative membrane-spanning domains. The nucleotide sequence of DNA immediately downstream of sefABC revealed a fourth open reading frame (ORF) designated seβ. This gene had the same translational polarity as sefABC (Figure 1). In fact, the AUG start codon for seβ overlapped the UGA stop codon of seβ. The gene organization of the gene cluster, has been confirmed on the chromosome by Southern blot analysis of Kpnl digested S. enteriditis 3b chromosomal DNA hybridized with sefA and seβ specific probes. Preceding the seβ ORF by 8 bp was a consensus Shine-Dalgarno sequence for translation initiation (GGAG). The seβ ORF was 447 bp and the predicted molecular weight of the encoded protein, designated SefD, was 16,722 Daltons. The predicted amino acid sequence of SefD had a putative signal peptidase cleavage site between Ser-24 and Ser-25 as determined by the method of von Heijne (1984). The presence of a putative leader sequence suggested that the protein was exported from the cytoplasm to either the periplasmic space or the outer membrane. To confirm that sefABC encoded proteins of the predicted sizes, proteins were translated in vitro from pKXl. The plasmid-encoded proteins were labeled with 35S-methionine using a cell-free coupled transcription-translation system (Prokaryotic DNA-Directed Transcription-Translation System Kit, Amersham, Oakville, ON) according to the manufacturers' instructions. Plasmids carrying either the 5.3 kb fragment of the sef operon or deletions thereof (delB 15, delB23, delDlO) were used as DNA templates (Figure 8B). Plasmids purified by alkaline lysis (Sambrook et al., supra) were incubated with the other reaction components in a final reaction volume of 30 μl and incubated at 37°C for 30 min. Unlabeled methionine (5 μl) was added, the mixture was incubated a further 5 min and then the reaction was terminated by placing the reactions at 0°C. Ten μl of the reaction mixture was added to 2x Laemmli sample buffer (Laemmli, "Cleavage of structural proteins during the assembly of the head of bacteriophage T4," Nature 227:680-685, 1970) and then subjected to microdialysis (Marusyk and Sergent, "A simple method of dialysis of small volume samples," Anal. Biochem. 705:403-404, 1989) on Millipore filters (VFWP25, Millipore, Millipore Corp., Bedford, MA) for 10 to 15 min prior to SDS-PAGE analysis on 12% gels poured with a 5% stacking gel (Laemmli, supra). The acrylamide gel was fixed for 30 min in 7% acetic acid for 30 min, dried onto 3MM paper for 1 hour at 80°C and then exposed to X-Omat-AR5 film (Kodak, Rochester, NY) to visualize the labeled proteins. Several translation products were identified (Figure 8A, lane 2). The 14KMr protein was identified on Western blots as SefA (Figure 8A, lane 7). The 90KMr protein was identified as SefC. The 27K r protein was identified as SefB. The 70K, 44K and 40KMj- bands were likely minor degradation products of SefC because these bands were absent when pSCl, which contained a deletion in seβ, was used as the template (Figure 8A lanes 2 and 3). The 16KMr band seemed to be a minor degradation product of SefB as this band remained when pSCl was used as a template (Figure 8 lanes 2, 3). When the three DNasel deletion subclones, delB15, delB23 and delDlO, were each used as templates, the bands for SefB, SefC and their minor degradation products were absent (Figure 8A, lanes 4-6) indicating sefA and/or its upstream region is necessary for the expression of seβ and seβ, as was predicted from the DNA sequence analysis (Figures 1, 2). To confirm that translation of SefB and SefC was dependent on the presence of sefA and/or the region upstream of sefA, the transcription start sites for sefA, seβ and seβ were determined. Primer extension studies consistently revealed transcription start sites immediately upstream of sefA. These included two major extension products as well as several minor ones. When the primer extension reaction was performed at 50°C, a temperature expected to destabilize secondary structures, reverse transcriptase still stopped at all the sites with the same frequency suggesting that stem-loop structures were not blocking the migration of reverse transcriptase. No transcription start sites could be found immediately upstream of seβ or seβ (data not shown). These results indicated that the 5' end of the mRNA transcript of sefABC was initiated upstream of sefA. EXAMPLE 7 In vivo expression of assembled fimbriae in E. coli Immunogold labeling of S. enteritidis cells with polyclonal immune serum raised to purified SEF14 fimbriae revealed thin, filamentous organelles located on the cell surface (Figure 10 A). E. coli cells hosting pKXl or cos 48 were shown by Western blot analysis to produce SefA. To determine whether E. coli cells hosting pKXl or cos48 were assembling intact fimbriae, E. coli cells were grown in 2.5 ml of colonization factor antigen static broth culture (Evans et al., "Hemagglutination of human group A erythrocytes by enterotoxigenic Escherichia coli isolated from adults with diarrhea: correlation with colonization factor," Infect. Immun. 18:330-331, 1977) for 60 h at 37°C. Cells were then mounted on formvar-coated grids, incubated with immune serum to native SEF14 fimbriae, then labeled with protein A-gold (Auroprobe, Pharmacia, Uppsala, Sweden). Labeled cells were then negatively stained with ammonium molybdate. Immunoelectron microscopic examination of E. coli HB101 containing cos48 revealed the presence of immunogold-labeled SΕF14 fimbriae on the cells surface (Figure 10B). Similar experiments demonstrated SEF14 fimbriae were produced in E. coli containing a cloned 10 kb -Kpnl fragment encoding sefU2U ] ABCD. Examination of E. coli JM109 carrying pKXl revealed the formation of surface blebs that were specifically gold labeled (Figure 10C). E. coli carrying 44 kb of S. enteritidis DNA (cos48) encompassing the sefABC operon displayed intact fimbriae, conversely, E. coli carrying the 5.3 kb Hindm fragment subcloned from cos48 showed that distinguishable SΕF14 filamentous fimbriae were not assembled, thus indicating that additional fimbrial genes are required for in vivo expression of assembled fimbriae. EXAMPLE 8 Co-Expression Of The SefA. SefB and SefC Genes seβ encodes a chaperone protein capable of preventing premature polymerization of fimbrial subunits in the periplasm. seβ can be used to chaperone the SefA protein, including the SefA protein fused to a foreign gene product (preferably comprising a foreign antigen) through the inner membrane to the periplasm, where the protein is ushered out of the cell by sefC. Such a foreign gene product can also be incorporated in a SEF14-like fimbrial structure. A 10 kb Kpnl fragment from cos48 is cloned into pUC19. The resulting clone is transformed into a competent E. coli or Salmonella host cell. To demonstrate expression, the host cells are disrupted and subjected to Western blot analysis using antisera to SefA, SefB and SefC proteins. The supernatant (prior to cellular disruption) is also subjected to Western blot analysis using antisera to SefA protein. To effect transport of protein to the supernatant without requiring the expression of seβ, a 1.5 kb Bsml fragment isolated from pTZ19 piHI, is blunted using T4 DNA polymerase and cloned into the Smal site of pUC19. The EcόRSJHindlΩ. fragment of this clone is ligated into the EcόRI/Hind→Jl sites of pINHIl 1 -B1 to create a construct where transcription of sefAseβ is initiated from the strong Ipp promoter, which promoter is under control of the lac operator. To demonstrate expression of the genes in E. coli, the resulting plasmid is transformed into a "leaky" E. coli strain known in the art. Expression is induced from the lac operator by the addition of IPTG. Western blot analysis of disrupted cells using antisera to SefA and antisera to SefB shows that both proteins are produced in the E. coli. EXAMPLE 9 Production of Protective Antibodies to Salmonella enteritidis In a preliminary experiment, outbred female mice were immunized with 5 x 10 5 S. enteritidis-3b by interperitoneal injection (IP) on day 0. Blood samples were collected at 10 and 20 days. Western blot analysis indicated that serum antibodies were generated to SefD (SEF18) but no detectable antibodies were found to the other fimbrins. Whole cells of wild type S. enteritidis 3b, an LPS o-polysaccharide deficient strain (3b TιψhoA-9) and a SEF17-deficient strain (3b TiψhoA 2-1 f) were grown under various conditions (T medium, 37°C, 24h; CFA broth, static, 37°C, 48h; LB broth, aerated, 37°C, 24h) to variably express the four fimbrial types SEF14, SEF17, SEF18, and SEF21. Cells were harvested by centrifugation, washed in PBS, resuspended to an ODβsonm of 2.0, treated with a final concentration of 3.5% formaldehyde and, incubated overnight at 4°C, the cells were then washed 5 times in PBS, then resuspended to an OD 6 5 0 nm of 1.0. These whole cell bacterins were injected into three week old turkeys using Alhydrogel as an adjuvant. The turkeys were boosted 7 and 14 days later and then bled. The serum was tested for antibodies against all four fimbrial types on Western blots and it was found that the turkeys made antibodies to SEF14, SEF17 and SEF18. Purified SEF14, SEF17 and SEF21 were used to raise monoclonal antibodies using standard monoclonal antibody generation techniques (Harlow and Lane, supra). Several monoclonal antibodies were generated to SEF14 (total of 8), SEF17 (total of 2) and SEF 21 (total of 5). One of the monoclonal antibodies generated to SEF14 and two generated to SEF21 were found to be of isotype IgA. This indicates that some fimbriae may specifically illicit a secretory antibody response, which can be advantageous for a vaccine directed toward Salmonella, an enteric pathogen. EXAMPLE 10 Production of polyclonal antibodies to Fimbriae A standard immunization protocol has been used to raise rabbit polyclonal antibodies to each of the four fimbrial types, namely; SEF 14, SEF 17, SEF 18 and SEF21. Purified, insoluble fimbriae were obtained as previously described (Collinson et al., supra), resuspended in phosphate buffered saline and emulsified with Freund's complete adjuvant prior to subcutaneous and intramuscular injection of a 1- month-old female New Zealand White rabbit. The rabbit was subsequently boosted at 1 or 2 week intervals with 50 to 500 μg protein emulsified in Freund's incomplete adjuvant. When the antibody titers were sufficiently high, the serum was collected. These serum antibodies were shown numerous times, via Western blotting techniques, to bind to their respective purified fimbrin subunits, and to bind the native fimbriae on whole cells as ascertained by immunoelecton microscopic observation of protein A gold- labelled fimbriae. EXAMPLE 11 Creation of a sefA (SEF 14) Mutant pDRA, which contains a Dr l fragment encompassing the sefA gene of S. enteritidis inserted in the Smal site of pT7T318, is digested with EcoO109I. Two oligonucleotides, LKC3A and LKC3B (Table 1, infra) are synthesized, annealed together, phosphorylated and ligated to EcoO109I-digested pDRA to inactivate sefA. The pDRA::LKC3 construct is digested with BgHl to remove multiple linkers and Sephaglas™ purified following agarose gel electrophoresis. Self-ligation of this construct results in the generation of pKCS2 which contains sefA inactivated with a single linker. pKCS2 is digested with EcoRI and Hin U to remove the sef A::LKC3 fragment which is then purified prior to electroporation. To insertionally inactivate sefA with a kanamycin (Km) resistance gene, linearized pDra is blunt-ended using the Klenow fragment and ligated to the 1.55 kb Fspl fragment of pKΕM containing the kanamycin resistance gene. The resulting plasmid, pKCSl, was digested with EcoRI and HincΩ. to cut out the sefA ::Km fragment which is purified prior to electroporation. S enteritidis 3b is transformed with the insertionally inactivated sefA gene fragment by electroporation to permit chromosomal sefA gene replacement by homologous recombination. Transformants are selected on media containing kanamycm for those transformed or screened for the inability to produce SefA or SΕF14 for those transformed with the./wWi4::LKC3. The constructs are confirmed by PCR and DNA sequencing or Western blot analysis. This method can also be applied using cloned and sequenced chromosomal sefA encoding DNA fragments from S. enteritidis (or S. berta, S. dublin, S ' gallinarum, or S. pullorum). EXAMPLE 12 Creation of an agfA (SEF 11) Mutant The plasmid pW3, which carries a 394 bp agfA fragment, containing a unique Xcml site at bp 156, is digested with Xcml, and the linearized plasmid is purified by agarose gel electrophoresis and Sephaglas™ treatment. Two oligonucleotides, LKC1A and LKC1B (see Table 1), synthesized on a Model 391 PCR-Mate™ DNA synthesizer (Applied Biosystems, Mississauga, ON), are mixed and annealed to create a double-stranded DNA fragment, LKC1, with 'sticky-ends' complementary to those generated by Xcml digestion. LKC1, which contains a BglR cleavage site, is phosphorylated using T4 polynucleotide kinase (Pharmacia P-L Biochemicals, Inc., Piscataway, NJ) (Sambrook et al. 1989) and ligated to .Λfc/wl-digested pW3 to insertionally inactivate agfA. BglR is used to digest pW3 carrying multiply ligated linkers. Following purification, pW3 carrying the BglR digested linkers is self-ligated to generate pKCAl. Alternatively, pW3 carrying the BglR digested linkers was mixed with the 3.4 kb H/wdm fragment of pHP45ΩCm (carrying a chloramphenicol resistance gene) to generate pKCA2. The resulting insertionally inactivated agfA gene fragment is cut from pKCAl or pKCA2 using EcoRI and purified. S enteritidis 3b is transformed with the insertionally inactivated agfA fragment by electroporation to allow chromosomal gene replacement by homologous recombination. The transformants are selected on media containing chloramphenicol for those transformed with agfA::Ω.Cm or on T-medium containing Congo red for the transformants containing agfA.±KCl. The genotype and phenotype of the agfA' transformants are confirmed by PCR and DNA sequencing or Western blot analysis, respectively. This method can also be applied using cloned and sequenced chromosomal DNA fragments from S. enteritidis which encode larger agfA flanking sequences to promote higher frequency of gene replacement by homologous recombination. EXAMPLE 13 Creation of a sefD (SEF18) mutant pSCC carries an S. enteritidis seβ gene fragment flanked EcoRI and Pstl sites. There are no unique internal restriction sites in seβ, so PCR is used to generate an internal Bam l site by site-specific mutagenesis. The primers KC6 and KC48 are used to amplify by PCR the 263 bp fragment. The product is digested with EcoRI and BamlR, purified and cloned into EcόRI/BamH digested pUC18 to generate pKCDl. A second set of primers, KC5 and KC47, are used to amplify the 333 bp fragment. The product is digested with BamJrE and Λl,purified, and cloned into Bam rR/Pstl digested pKCDl to generate pKCD2. The 2.0 kb BamΗ ΩSm/Spc fragment from pHP45Ω (which contains streptomycin and spectinomycin resistance genes) is cloned into BamΕR digested pKCD2 to generate pKCD3. The EcόRI/BamΗ fragment of pKCD3 is purified prior to electroporation. The seβ gene containing the engineered BamHL site is also insertionally inactivated using LKC2 linkers converted to LKC4 by digestion with BglR. S enteritidis 3b is transformed with the resulting insertionally inactivated seβ fragment, seβ: :ΩSmSpc, or seβ::l→KC4 by electroporation to permit chromosomal gene replacement. The transformants are selected on media containing spectinomycin and streptomycin for those transformed with sc/D::ΩSpcSm or screened for the inability to produce SefD for those transformed with the seβ:±KC4. The genotype and phenotype of the seβr transformants are confirmed by PCR and DNA sequencing or Western blot analysis, respectively. This method can also be applied using cloned and sequenced chromosomal DNA fragments from S. enteritidis which encode larger flanking sequences around seβ and therefore increase the frequency of homologous gene replacement. EXAMPLE 14 Creation of ' a FimA (SEF21) mutant A 171 bp HiriPl fragment of fimA previously subcloned into the unique Accl site of M13mpl8 is cut from the replicative form by double digestion with BamΗL and Hm-XTR. Υ\ sfimA fragment is subcloned into BamWR and HindlE digested pUC18 to generate pKCFl. Two complementary oligonucleotides, LKC2A and LKC2B (Table 1), are synthesized, annealed together and then phosphorylated with T4 polynucleotide kinase to generate the double-stranded linker LKC2 which contains an internal BglR site and possessed sticky ends compatible with those generated by -ftrfBI digestion. pKCFl is digested with BstBl, purified by agarose gel electrophoresis and Sephaglas™ treatment, ligated to LKC2, digested with BglR and re-purified. pKCFl carrying the LKC2 linker is self-ligated to generate pKCF2. The./wnA::LKC2 fragment is cut from pKCF2 with BamΕR and Hrwdiπ and purified. To generate a fimA fragment insertionally inactivated with ΩTc, BstBl, linearized fragments of pKCFl and 1.9 kb H diπ fragments of pHP45ΩTc (carrying the tetracycline resistance gene (ΩTc)) are blunt-ended by treatment with the Klenow fragment of DNA poll and ligated to create pKCF3. Prior to introduction into S. enteritidis, the fimA::ΩTc fragment is cut from pKCF3 with EcoRI and HindlR and purified. S enteritidis 3b is transformed with the resulting insertionally inactivated fimA fragment by electroporation to allow chromosomal fimA gene replacement by homologous recombination. The fimA" transformants are selected on media containing tetracycline to select cells transformed with fimA:: ΩTc or screened for the inability to produce FimA or SΕF21 for those transformed with the./wra-4::LKC2. The genotype and phenotype of the fimA' recombinants are confirmed by PCR and DNA sequencing or Western blot analysis, respectively. This method can also be applied using cloned and sequenced chromosomal DNA fragments from S. enteritidis which encode larger flanking sequences around fimA and therefore increase the frequency of homologous gene replacement. Table 1 Oligonucleotide sequences for cloning and mutagenesis procedures of S. enteritidis fimbrial genes. Linker and Sequence primer names LKCl α LKC1A 5 'GCTAACAGAGTAAGATCTTGCTAACGAGCGG (SEQ. ID NO, LKC1B CCGATTGTCTCATTCTAGAACGATTGCTCGC 5 ' (SEQ. ID NO, LKC2 α LKC2A 5 'CGCTAAGCAGATCTAAACCCTAATCCC (SEQ. ID NO, LKC2B GATTCGTCTAGATTTGGGATTAGGGGC 5 ' (SEQ. ID NO, LKC3 α LKC3A 5 'GGCCTAATGACCTAAGATCTTGCTAACGAAT (SEQ. ED NO, LKC3B GATTACTGGATΓCTAGAACGATTGCTTACCG 5 ' (SEQ. ID NO, KC5 5 'GAGAGGGAAAAAGGATCCTCATTAGTTCAAG (SEQ. ID NO. KC6 CTCTCCCTTTTTCCTAGGAGTAATCAAGTTC 5 ' (SEQ. ID NO. KC48 5 'AGCGGATAACAATTTCACACAGGAAAC (SEQ. ID NO. KC47 5 'CGCCAGGGTTTTCCCAGTCACGAC (SEQ. ID NO. LKC4 α 5 'GATCTAAACCCTAATCCCCGCTAAGCA (SEQ. ID NO, ATTTGGGATTAGGGGCGATTCGTCTAG 5 ' (SEQ. ID NO._ a These linkers were designed to have TAA or TAG stop codons in all three frames so that insertion of this piece of DNA into a gene will cause premature termination of the protein as well as introducing a useful cloning site. EXAMPLE 15 In vivo expression of assembled fimbriae in E. coli Immunogold labeling of S. enteritidis cells with polyclonal immune serum raised to purified SΕF14 fimbriae revealed thin, filamentous organelles located on the cell surface (Figure 6A). E. coli cells hosting pKXl or cos48 were shown by Western blot analysis to produce SefA. To determine whether E. coli cells hosting pKXl or cos48 were assembling intact fimbriae, E. coli cells were grown in 2.5 ml of colonization factor antigen static broth culture (Evans et al., "Hemagglutination of human group A erythrocytes by enterotoxigenic Escherichia coli isolated from adults with diarrhea: correlation with colonization factor," Infect. Immun. 18:330-331, 1977) for 60 h at 37°C. Cells were then mounted on formvar-coated grids, incubated with immune serum to native SEF 14 fimbriae, then labeled with protein A-gold (Auroprobe, Pharmacia, Uppsala, Sweden). Labeled cells were then negatively stained with ammonium molybdate. Immunoelectron microscopic examination of E. coli HB101 containing cos48 revealed the presence of immunogold-labeled SEF 14 fimbriae on the cells surface (Figure 6B). However, examination of E. coli JM109 carrying pKXl revealed the formation of surface blebs that were specifically gold labeled (Figure 6C). E. coli carrying a 44 kb fragment of S. enteritidis DNA (cos48) encompassing the sefU2UjABCD operon, as well as E. coli carrying a 10 kb .Kpnl fragment subcloned from cos48, displayed intact fimbriae. Conversely, E. coli carrying a 5.3 kb HindJE fragment subcloned from cos48 showed that distinguishable SΕF14 filamentous fimbriae were not assembled. From the foregoing, it will be appreciated that, although specific embodiments of the invention have been described herein for purposes of illustration, various modifications may be made without deviating from the spirit and scope of the invention. Accordingly, the invention is not limited except as by the appended claims.

Claims: Claims 1. A composition able to elicit an immune response in an animal comprising an isolated protein selected from the group consisting of a SefC protein, a SefD protein, a TctC protein and an AgfA protein, in combination with a physiologically acceptable carrier or diluent. 2. A vector construct comprising a mutant gene selected from the group consisting of a mutant tctA gene, a mutant tctB gene and a mutant tctC gene, said mutant gene capable of inactivating the corresponding tricarboxylic acid transport pathway in Salmonella upon incorporation of said vector construct into said Salmonella, to yield an attenuated Salmonella. 3. A biologically pure attenuated Salmonella comprising a mutation in a gene selected from the group consisting a tctA gene, a tctB gene, and a tctC gene, to yield said attenuated Salmonella, wherein said mutation eliminates the function of the corresponding tricarboxylic acid transport system of said attenuated Salmonella. 4. A composition able to elicit an immune response in an animal comprising an attenuated Salmonella having an inactivating mutation in a gene or operon selected from the group consisting of a tctA gene, a tctB gene, a tctC gene, a tctl operon, a tctll operon and a tctlll operon, in combination with a physiologically acceptable carrier or diluent. 5. A composition able to elicit an immune response in an animal comprising an attenuated Salmonella having a mutation in two or more fimbriae encoding genes selected from the group consisting of sefA, seβ, agfA, and fimA, wherein said mutations effectively prevent production of fimbriae from said genes, in combination with a physiologically acceptable carrier or diluent. 6. The composition of any one of claim 4 or 5 able to elicit an immune response in an animal wherein said attenuated Salmonella is capable of expressing a foreign antigen in one or more of its fimbriae or in an aggregate. 7. The Salmonella of claim 6 wherein said attenuated Salmonella is capable of expressing a foreign antigen fused to a SefA, SefC, SefD, TctC, FimA, or AgfA protein. 8. An expression vector construct comprising a sefA gene, a seβ gene, seβ gene, a FimA gene, a tctC gene or an agfA gene operably linked in open reading frame to a foreign gene to yield a dicistronic gene product, said dicistronic gene product capable of being expressed in a fimbriae, or an aggregate comprising said gene product, of a Salmonella* 9. An expression vector construct comprising a sefA gene, a seβ gene, seβ gene, zfimA gene, a tctC gene or an agfA gene operably linked in open reading frame to a foreign gene to yield a dicistronic gene product, said dicistronic gene product capable of being expressed in a fimbriae, or an aggregate comprising said gene product, of an E. coli. 10. An expression vector construct comprising an agfA gene capable of producing inE. coli a stable fimbriae comprising AgfA protein. 11. A stable fimbriae comprising an AgfA protein fused to one or more foreign antigens. 12. A method of eliciting an immune response in an animal, comprising: (a) separating fimbriae comprising a SefA protein, a SefD protein, a FimA protein, or an AgfA protein fused to a foreign antigen grown on a Salmonella host cell from said Salmonella host cell; and (b) introducing said fimbriae into said animal in conjunction with a physiologically acceptable carrier or diluent. 13. A method of eliciting an immune response in an animal to Salmonella, comprising: (a) separating an amino acid polymer comprising a SefA protein, a SefC protein, a SefD protein, a FimA protein, a TctC protein, or an AgfA protein fused to a foreign antigen grown on a Salmonella host cell from said Salmonella host cell; and (b) introducing said amino acid polymer into said animal in conjunction with a physiologically acceptable carrier or diluent. 14. A method of eliciting an immune response in an animal to Salmonella, comprising: (a) separating fimbriae comprising a SefA protein, a SefD protein or an AgfA protein grown on an E. coli host cell from said E. coli host cell; and (b) introducing said fimbriae into said animal in conjunction with a physiologically acceptable carrier or diluent. 15. A method of eliciting an immune response in an animal to Salmonella, comprising: (a) separating an amino acid polymer comprising a SefA protein, a SefC protein, a SefD protein, a TctC protein, or an AgfA protein grown on an E. coli host cell from said E. coli host cell; and (b) introducing said amino acid polymer into said animal in conjunction with a physiologically acceptable carrier or diluent. 16. The method of claim 14 or 15 wherein said protein is fused to a foreign antigen. 17. A method of eliciting an immune response in an animal to Salmonella comprising introducing into said animal one of the group consisting of an isolated SefD protein, an isolated SefC protein and an isolated AgfA protein, in combination with a physiologically acceptable carrier or diluent. 18. A method of eliciting an immune response in an animal to Salmonella, comprising introducing an attenuated Salmonella into said animal, said Salmonella comprising an ineffective gene or operon selected from the group consisting of a tctA gene, a tctB gene, a tctC gene, a tctl operon, a tctll operon, and a tctlll operon. 19. A method of eliciting an immune response in an animal comprising introducing into an animal an attenuated Salmonella having a mutation in two or more fimbriae encoding genes selected from the group consisting of a sefA, seβ, agfA, and fimA, wherein said mutations effectively prevent production of fimbriae from said genes, in combination with a physiologically acceptable carrier or diluent. 20. The method of claim 18 or 19 wherein said attenuated Salmonella expresses one or more foreign antigens, said foreign antigens eliciting an immune response from said animal. 21. The method of claim 20 wherein said one or more foreign antigens are located on a fimbriae of said attenuated Salmonella. 22. A method of eliciting an immune response in an animal to Salmonella comprising introducing an E. coli mto said animal, said E. coli expressing Salmonella fimbriae. 23. The method of claim 22 wherein said Salmonella fimbriae comprise agfA gene product. 24. The method of claim 22 wherein said Salmonella fimbriae further comprises a foreign antigen, said foreign antigen capable of eliciting an immune response from said animal. 25. A method of eliciting an immune response in an animal to Salmonella comprising introducing a vector into said animal wherein said vector comprises a gene selected from the group consisting of & seβ gene, seβ gene, tctC, and an agfA gene.

Inventors: CLOUTHIER SHARON C, COLLINSON S KAREN, DORAN JAMES L, KAY WILLIAM W, CLOUTHIER, SHARON, C., COLLINSON, S., KAREN, DORAN, JAMES, L., KAY, WILLIAM, W.
Applicants: KING JOSHUA, UNIV VICTORIA INNOVAT DEV, KING, JOSHUA, UNIVERSITY OF VICTORIA INNOVATION AND DEVELOPMENT
Application year: 1994
Main classification: C12N15
IPC codes: A61K39, C07K14, C07K16, C12N15, C12P21, C12Q1